Radio communication system and radio communication method

ABSTRACT

A radio communication system for carrying out communications between radio stations by modulating a plurality of signal sequences to be transmitted and received into at least one frequency channel assigned to each of a plurality of cells is formed by a channel mapping means for rearranging for each cell a plurality of frequency channels assigned with respect to each cell, and newly assigning particular frequency channels as a transmission and reception band of said signal sequences, and a bandwidth control means for controlling a bandwidth of said assigned frequency channel according to a propagation state of said assigned frequency channel.

TECHNICAL FIELD

The present invention related to a radio communication system and aradio communication method at a time when radio base stations and aplurality of mobile communication terminal stations carry outcommunications through multiplexed channels, which are used for digitaltransmission in an orthogonal frequency division multiplexing modulationscheme such as the OFDM scheme and the fourth generation scheme.

BACKGROUND ART

(A) About the Digital Cellular System

In the conventional digital cellular systems (PDC: Personal DigitalCellular telecommunication system, PHS: Personal Handy-phone System,GSM: Global System for Mobile communications, for example), the radiobase stations and a plurality of mobile communication terminal stationscarry out communications through time division multiplexed (TDMA) radiochannels. In these systems, each radio station is assigned with a fixedfrequency channel such that no interferences with neighboring basestations occur, and a plurality of mobile communication terminalstations and the radio base stations can carry out communicationswithout causing interferences, by using channels formed by the frequencychannels as a plurality of time division multiplexed (TDMA) channels.

In such a conventional radio communication system, in a case where acovered area by each base station has a multi-cell configuration, aradio communication for connecting a radio base station and a mobilecommunication terminal station within each cell, for example, is carriedout though a channel frequency channel assigned to each base station.Then, in the radio communication in the FDMA or TDMA cellular scheme, inorder to avoid the neighboring cell interferences, the frequency channelarrangement is made such that the identical frequency channel will notbe used at the neighboring cells. Such conventional frequency channelassignment methods includes the following.

(1) Fixed Frequency Channel Assignment

In the fixed frequency channel assignment (FCA: Fixed ChannelAssignment), the radio frequency channel that can be selected isdetermined fixedly for each radio cell, and it is configured such thatthe reuse of the radio frequency channel is realized with an optimaldistance interval. The arrangement is made by determining the frequencychannel to be arranged to each cell in advance, so that this is calledthe fixed frequency channel assignment method.

(2) Dynamic Frequency Channel Assignment

There is a method for dynamically rearranging the frequency channel tobe assigned and arranged to each cell according to a traffic of eachcell, with respect to said fixed frequency channel arrangement. This iscalled the dynamic frequency channel assignment. In this method, at eachradio cell, all the frequency channels used by the system can beselected. Namely, as long as a required quality is satisfied, it can beused for communication at any radio cell.

In the dynamic frequency channel assignment method, there are advantagesthat

(a) the efficient utilization of frequencies according to coarse/denseof the traffic can be realized, and

(b) compared with the fixed frequency channel arrangement, the design iseasier as there is no need to make the radio frequency channelarrangement plan before the start of the system operation.

(B) About the Frequency Orthogonal Multiplexing Scheme (OFDM)

On the other hand, in recent years, the multi-carrier transmissionscheme is attracting attentions as a measure against the frequencyselective fading in the high speed transmission. In this multi-carriertransmission scheme, the transmission data are transmitted by beingdistributed to a plurality of carriers with different frequencies, sothat the band of each carrier becomes a narrow band, and it is harder toreceive an influence of the frequency selective fading when the numberof sub-carriers is larger. In particular the orthogonal frequencydivision multiplexing (OFDM: Orthogonal Frequency Division Multiplexing)in which respective sub-carriers are orthogonalized has a high frequencyutilization efficiency and it is used for the radio LAN and digitalbroadcasting.

In this scheme, the frequencies of respective carriers are set such thatrespective carriers are mutually orthogonalized within a symbol section.The spectra of the OFDM signals are continuously overlapping with eachother, and a processing to take out the signal on a particular carrierby using a band pass filter as in the ordinary multi-carriertransmission is not carried out. Then, in the OFDM, theorthogonalization of respective carriers and the extraction of eachsub-carrier signal are carried out by using an inverse discrete Fouriertransform (IDFT: Inverse Discrete Fourier Transform) circuit and adiscrete Fourier transform (DFT: Discrete Fourier Transform) circuit ingeneral.

Then, in the reception in this OFDM scheme, the data symbol is correctlytaken out by the demodulation from each extracted sub-carrier, so thatunlike the multi-carrier transmission in which a plurality ofsub-carriers are arranged on a frequency axis by providing guard bandsand each sub-carrier is separated by a narrow band filter, the frequencyintervals of respective sub-frequency channels can be narrowed byoverlapping them and therefore the frequency utilization efficiency isgood in the OFDM.

The power spectrum of the general frequency division multiplexing schemeis, as shown in FIG. 1, formed by the arrangement of the occupied bandswhich are bands necessary for transmitting signals of respectivesub-carriers and guard bands for preventing interferences betweenrespective sub-carriers. In other words, the entire band used in theentire system is (Occupied band of the frequency channel)×N+(Guardband)×(N−1).

In the OFDM, the orthogonality between respective carriers is maintainedand the overlap of respective modulated wave bands is made possible bysetting the frequency interval of the sub-carrier to the interval of thefirst theorem of Nyquist. Namely, as shown in FIG. 2, the orthogonalizedOFDM signal is such that the symbol can be taken out despite of the factthat the spectra of respective sub-carriers are overlapping, so that thefrequency channel separation of the sub-carrier can be made narrow. Inother words, the entire band used in the entire system is only (Occupiedband of the frequency channel)×(N+1)/2.

In FIG. 3, a configuration of the conventional OFDM radio device usingthe inverse discrete Fourier transform circuit is shown. In FIG. 3, thedata sequence to be transmitted is first applied with the basebanddigital modulation by the symbol mapper 1. It is converted into aplurality of frequency channels of the identical symbol rate by theserial to parallel converter 2, and it is converted into a plurality oforthogonalized sub-carrier signals by carrying out the inverse Fouriertransform by the inverse discrete Fourier transform circuit 4. Theparallel output signals of the inverse Fourier transform circuit 4 are,the time series transmission signals are converted into the time seriestransmission signals by applying the serial to parallel conversion atthe parallel to serial converter 5. They are converted into the RFfrequency band used by the system at the radio transmitter 6, and afterthe power is amplified, they are transmitted through the transmissionantenna 7.

Examples of the communication system in which the OFDM is introducedincludes the radio LAN system using 5.2 GHz band, etc. In this system,52 sets of the sub-carriers are used.

The OFDM has features such as the interferences between codes can befurther reduced by setting the guard interval in the symbol section.

Also, usually, the sub-carrier is secured by the continuous band, In theOFDM transmission, the orthogonality between respective sub-carriers isvery important, and if the orthogonality of frequencies is broken evenslightly, the inter-carrier interference (ICI: Inter-CarrierInterference) occurs between sub-carriers, and it has a large influenceon the signal transmission characteristics.

In the OFDM system used in the digital broadcasting, the orthogonalitybetween respective sub-carriers is secured, and in the case of carryingout the plural station simultaneous transmission at the identicalfrequency channel, the sufficient synchronization is established betweencarries of the transmitter of each transmission site, and the sending ofthe broadcast signals is carried out such that the orthogonality can besecured sufficiently.

(C) About the Cellular System and the OFDM

As an example of applying the OFDM to the radio communication system,the radio communication system using the band division multiple access(BDMA: Band Division Multiple Access) scheme has been proposed, forexample. The spectrum of the BDMA scheme is shown in FIG. 4. The BDMAscheme is a communication scheme which uses both the frequency divisionmultiple access and the time division multiple access. In the BDMAscheme, the information transmission is carried out by applying thelinear digital modulation such as QPSK to each sub-carrier. In thisscheme, the entire transmission band is divided into a plurality ofsub-bands, and they are assigned to different users in units of thedivided sub-bands. Also, in Japanese Patent Application Laid Open No.H10-191431, it is proposed to increase or decrease the number ofsub-carriers according to the transmission capacity required by the userin the multi-carrier transmission.

(D) About the CDMA Scheme

In the case of the CDMA, the arrangement of the identical frequencyrepeating cells is theoretically possible, but in the case where aplurality of micro-cells which communicate by using the identicalfrequency band exists within a macro-cell, the DSA (Dynamic Frequencyarrangement: Dynamic Spectrum Allocation) is still necessary as ameasure against the identical frequency channel interference withincell.

Now, in this CDMA scheme, there are cases of adopting the hierarchicalcell structure such as that in which the micro-cells are located withinthe macro-cell, and in order to utilize frequencies efficiently in thishierarchical cell structure, there is a proposition for a method inwhich, in a system in which the identical frequency band is shared bysystems with different transmission speeds for the micro-cell and themacro-cell, for example, when one of the frequency channels becomesunnecessary, a permission for use is given to one with the low prioritylevel among the other one of the vacant frequency channel, and apartition which is a boundary between the frequency band of themicro-cell side and the frequency band of the macro-cell side is shifted(see Japanese Patent Application Laid Open No. H11-205848, for example).

However, in the conventional system such as the digital cellular schemeexplained in the above described (A), there is a need to secure aplurality of frequency channels, and arrange them by providing aconstant interval so as to avoid the interference of the identicalfrequency channels in the frequency channel assignment.

Consequently, it is utilized efficiently by assigning respectivefrequency channels to respective cells in the limited frequency bandassigned to the system, but in the future the shortage of the number offrequency channels due to the increase of the data communication trafficis expected, and the radio communication system with the higherfrequency utilization efficiency is demanded.

Also, in the OFDM explained in the above described (B), there is a needto secure the frequency channel band in which the sub-carrierssatisfying the orthogonality condition are arranged continuously, asshown in FIG. 5. For this reason, the channel assignment is going to beregulated, and in the case of the shortage of the frequency channels, itis considered that it becomes difficult to deal with it flexibly.

On the other hand, in the digital broadcasting and the radiocommunication explained in the above described (C), a plurality ofdelayed waves with large time delays arrive due to the multi-pathpropagation, so that in the high speed transmission of information, thetransmission speed required for the radio communication largely changesaccording to the user and the application, as from speech, electronicmails, still images, video image transfer, etc. Consequently, in thecase of carrying out the information transmission by the bands that aredivided and determined in advance as in the conventional radiocommunication system, the division loss becomes large, and there is aproblem regarding the efficient utilization of frequencies.

In addition, in the CDMA scheme explained in the above described (D),even in the method for realizing the efficient utilization of frequencychannels by shifting the partition, the total sum of the number ofchannels that can be secured in the system band is constant for themacro-cell and the micro-cell, and it is possible to consider the caseswhere the shortage of channels on one side cannot be compensated bychannels of the other side by simply shifting the partition.

(Description of the Frequency Orthogonalized Multiplexing Scheme (OFDM))

Conventionally, the the multi-carrier transmission scheme has beenproposed as a measure against the frequency selective fading in the highspeed digital transmission. In this multi-carrier transmission scheme,the transmission information data is sent by being distributed to aplurality of sub-carriers with different frequencies, so that the bandof each carrier can be a narrow band, and there is a characteristic thatwhen the bands of these sub-carriers are narrower, it is harder toreceive an influence of the waveform distortion due to the frequencyselective fading.

In such a multi-carrier transmission scheme, particularly in theorthogonal frequency division multiplexing (OFDM: Orthogonal FrequencyDivision Multiplexing) in which respective sub-carriers areorthogonalized, unlike the conventional multi-carrier transmission inwhich a plurality of sub-carriers are arranged on the frequency axis byproviding guard bands and each sub-carrier is separated by a narrow bandfilter, the frequency utilization efficiency can be made higher bynarrowing the frequency intervals of respective sub-frequency channelsby overlapping them, and it is used for the radio LAN and the digitalbroadcasting.

In this scheme, the frequency intervals of respective sub-carriers areset such that respective sub-carriers become orthogonal to each otherwithin the symbol section. Then, in the OFDM, in practice, theorthogonalization of respective sub-carriers and the extraction of eachsub-carrier signal are carried out by the digital signal processing,using the inverse discrete Fourier transform (IDFT: Inverse DiscreteFourier Transform) circuit and a discrete Fourier transform (DFT:Discrete Fourier Transform) circuit.

(Description of the OFDM Function Block)

FIG. 3 is a block diagram showing a structure of a conventional OFDMradio device equipped with an inverse discrete Fourier transformcircuit.

As shown in FIG. 3, the conventional OFDM radio device has a symbolmapper 1 for applying the baseband digital modulation with respect tothe information data sequence of the user, a serial to parallelconverter 2 for converting the output signal of the symbol mapper 1 intoa plurality of channels with the identical symbol rate, an inversediscrete Fourier transform circuit 4 for applying the inverse Fouriertransform with respect to the parallel output signal sequences which areoutput signals of the serial to parallel converter 2 and converting theminto a plurality of orthogonalized sub-carrier signals, a parallel toserial converter 5 for converting the output signals of the inversediscrete Fourier transform circuit 4 into a time series signal, and aradio transmitter 6 for converting it into an RF frequency band used bythe system and amplifying the power.

In such a conventional OFDM radio device, assuming that the informationdata sequence to be transmitted is a, the digital modulation such asQPSK, QAM, for example is carried out by the symbol mapper 1 first. Bythis digital modulation, the information bit sequence is converted intoa complex symbol sequence S_(x) (S₀, S₁, S₂, S₃). Next, it isdistributed to a plurality (N sets) of sub-carrier channels (F₁, F₂, . .. F_(N)) by the serial to parallel converter 2. Then, the inverseFourier transform is carried out by the inverse discrete Fouriertransform circuit 4, and they are converted into time series samplevalues (sample values of OFDM symbols) in which a plurality oforthogonalized sub-carrier frequency channel signals are superposed. Thesample values of the OFDM symbols are serial to parallel converted bythe parallel to serial converter 5, and converted into the continuoustime series transmission signal, and after it is frequency convertedinto the RF frequency band used by the system at the radio transmitter6, the power is amplified, and it is transmitted from the transmissionantenna 7.

(Transmission Band Variable of the OFDM)

In the ordinary OFDM transmission device, the system clock frequency isfixed, so that the bandwidth is constant. For example, Japanese PatentApplication Laid Open No. H11-215093 proposes a configuration for easilycarrying out variable of the band frequency of the sub-carrier, and anaddition of a function for automatically following variable of the bandof the sub-carrier at a receiving side, in the transmission of the OFDMsignals.

Describing it in detail, as shown in FIG. 6, in the OFDM transmissiondevice disclosed in Japanese Patent Application Laid Open No.H11-215093, at the transmitting side, a clock output terminal of a clockoscillator 101B is connected to a clock rate conversion unit 101A, and aclock output terminal of the clock rate conversion unit 101A isconnected to respective clock terminals of a rate conversion unit 101,an encoding unit 102T, an IFFT unit 103A, a guard attaching unit 103B, asynchronization symbol insertion unit 105, and an orthogonal modulationprocessing unit 108. At the receiving side, an output VC of asynchronization detector 109A is connected to a terminal VC of a clockoscillator 109B, and an output FSTr of the synchronization detector 109Ais connected to FST terminals of an FFT unit 103C and a rate inverseconversion unit 107. Also, an output CKr of the clock oscillator 109B isconnected to clock CK terminals of the FFT unit 103C, the rate inversionconversion unit 107, an orthogonal demodulation processing unit 109, andthe synchronization detector 109A.

Then, in such an OFDM transmission device disclosed in Japanese PatentApplication Laid Open No. H11-215093, the clock rate conversion unit foruniformly changing the operation timing of the transmission unit and theperiod of the clock that determines the clock rate is provided, and afunction for controlling the reproduction clock rate according to thedetected frame information period is added to the receiving side, andthe frequency channel that can be used and the bandwidth that can beused are determined by checking the radio wave using state (how vacantthe channels are).

Also, in Japanese Patent Application Laid Open No. 2000-303849, theflexibility and the adaptability of the OFDM system are given by makingit possible to carry out the increasing/decreasing adjustment (scaling)for the operation parameters or characteristics of the system such asthe symbol length of the OFDM, the number of carriers, or the number ofbits per symbol of each carrier, for example, by the external setting orthe decoded date.

The scaling control circuit of that OFDM system provides thecompatibility or the desired performance by dynamically changing theoperation parameters or characteristics according to the case of judgingnecessary or effective.

Also, in Japanese Patent Application Laid Open No. 2000-303849, thescaling of the OFDM parameter is carried out by the external setting orthe decoded data. The scaling uses information such as a received signalstrength, a ratio of the noise plus interference with respect to thereceived signal, a detected error, a notice, etc.

The influence of the multi-path in the case of adding the guard band isshown in FIG. 7. The advantage of providing the guard interval to themultiplexed carrier transmission is that it becomes possible to reduceor remove the inter-symbol interference (inter-code interference) doe toa signal dispersion (or a delay spread) in the transmission channel, asan interval as a guard time Tg is inserted while transmitting a nextsymbol and there is no need for a waveform equalizer that is necessaryin the single carrier system.

The delayed copy for each symbol that arrives to a receiver after theintended signal can disappear before the next symbol is received, by theexistence of the guard time. As such, the advantage of the OFDM lies inthe function for overcoming the adverse influence of the multiplexedchannel transmission without requiring the equalization.

In Japanese Patent Application Laid Open No. H11-215093 described above,the frequency that can be used and the bandwidth that can be used aredetermined by checking the radio wave using state (how vacant thechannels are). However, in the actual mobile communications, the radiowave propagation path varies in time and its property changes largely.In the mobile communication propagation path, the following pointbecomes problematic by the delayed waves due to the time variation ofthe propagation path and the multi-path propagation, and there is aproblem that the signal transmission characteristics are degraded.

By using FIG. 8, the relationship between the sub-carrier occupiedbandwidth and the time variation of the fading will be described. Notethat, the influence of the Doppler shift will be described as an exampleof the time variation of the fading.

In the mobile communication, the amount of the Doppler shift isdetermined by the moving speed of the mobile station itself, the movingspeed of an object which reflected arriving radio waves, etc. Ingeneral, when the mobile station runs through the multiplexed wavepropagation path, the received waves change randomly depending on thewavelength λ of the transmission waves and the moving speed V of themobile station. Each element wave is Doppler shifted as much asV/λ=f_(D) at maximum, and the spectrum spreading appears.

Here, assuming that the occupied frequency bandwidth of the narrow bandsub-carrier (FIG. 8(a)) is B₁, the occupied bandwidth of the wide bandsub-carrier (FIG. 8(b)) is B₂, and the maximum Doppler shift amount isD_(S), in the OFDM transmission in general, when the relative value ofthe Doppler shift amount D_(S) with respect to the sub-carrier occupiedbandwidth B becomes larger, the orthogonality between sub-carriers isdeteriorated, and the signal transmission characteristics are degradeddue to the inter-channel interference (ICI: Inter-Channel Interference).Namely, compared with the case where the occupied bandwidth of thesub-carrier is narrow (B₁) as shown in FIG. 8(a), a rate (D_(S)/B_(W))of the Doppler shift with respect to the sub-carrier band issufficiently small in the case where the occupied bandwidth is wide(B₂), so that the degradation of the transmission characteristics due tothe Doppler shift is less.

However, when the band of the sub-carrier is wide, it becomes easier toreceive the influence of the frequency selective fading due to themulti-path propagation. The frequency characteristics of the radio wavepropagation path are affected largely by the propagation delay time, andwhen the maximum delay time τ_(max) is large, the frequencycharacteristicd at the propagation path is distorted largely.

In contrast, as shown in FIG. 9, in the case where the occupiedbandwidth of the sub-carrier is narrow as B₁, it can be regarded as theuniform fading in each sub-carrier, and only the received signal levelsof a part of the sub-carriers are lowered, so that it can be recoveredto some extent by the gain adjustment by an AGC (Automatic Gain Control)circuit.

However, in the case where the occupied bandwidth of the sub-carrier iswide as B₂, the received signal levels of a part of the occupied banddrop frequency selectively due to the frequency selective fading, sothat there has been a problem that the waveform distortion occurs andthe signal transmission characteristics are considerably degraded.

Consequently, even in the case of carrying out the transmission with theidentical information bit rate, the optimum sub-carrier bandwidth andthe number of sub-carriers are different due to the time variation ofthe fading and the maximum delay amount. Also, in the case where themaximum tolerable bandwidth assigned to each user is constant, when eachsub-carrier occupied band is widened, as shown in FIG. 10, there arisechannels which deviate from the maximum tolerable bandwidth.

On the other hand, in the Japanese Patent Application Laid Open No.2000-303849 described above, the scaling is carried out dynamically bythe external setting or the decoded data. In other words, in order toavoid the frequency selective fading or the like in which the locationfactor is dominant, there has been a problem that there is a need tocarry out the scaling by making some setting at each time of moving.

In addition, in the VSF-OFCDM scheme (Variable SpreadingFactor-Orthogonal Frequency and Code Division Multiplexing) which is theso called fourth generation communication scheme, the information symbolis divided on a plurality of frequency axes, and the information symbolis transmitted by spreading it by the spread code of the variablespreading rate assigned to each mobile station, so that the symbol ratewill be different from the other conventional transmission schemes sothat the interferences between different transmission scheme occur in aregion where the other transmission schemes coexist, and it is expectedthat the identical frequency band cannot be shared.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a radio communicationsystem and a radio communication method capable of utilizing thefrequency band efficiently, in the case where the frequency bandsrespectively utilized in a wide band system of the OFDM scheme and anarrow band system coexist.

Another object of the present invention is to provide a radiocommunication system and a radio communication method capable ofutilizing the frequency channels within the band efficiently, at a timeof carrying out communications between radio stations through thefrequency channel assigned to each of a plurality of areas of thedigital cellular system, the frequency orthogonalized multiplexingscheme system, CDMA scheme, etc.

Another object of the present invention is to provide a radiocommunication system and a radio communication method capable ofrealizing the improvement of the transmission characteristics, bycontrolling the sub-carrier bandwidth and the number of sub-carriers, bycalculating the optimum sub-carrier occupied band according to thefading (radio wave propagation path) information.

The present invention provides a radio communication system for carryingout communications between radio stations by modulating a plurality ofsignal sequences to be transmitted and received into at least onefrequency channel assigned to each of a plurality of cells, a radiocommunication system characterized by having a channel mapping means forrearranging for each cell a plurality of frequency channels assignedwith respect to each cell, and newly assigning particular frequencychannels as a transmission and reception band of said signal sequences,and a bandwidth control means for controlling a bandwidth of saidassigned frequency channel according to a propagation state of saidassigned frequency channel.

Also, the present invention provides a radio communication method forcarrying out communications between radio stations by modulating aplurality of signal sequences to be transmitted and received into atleast one frequency channel assigned to each of a plurality of cells, aradio communication method characterized by having a step forrearranging for each cell a plurality of frequency channels assignedwith respect to each cell, and newly assigning particular frequencychannels as a transmission and reception band of said signal sequences,and a step for controlling a bandwidth of said assigned frequencychannel according to a propagation state of said assigned frequencychannel.

Moreover, in the present invention, at a time of carrying outcommunications between radio stations through the frequency channelassigned to each of a plurality of areas, rearrangement of assignment ofsaid frequency channels is carried out, and particular continuousfrequency channels of a system band are assigned for each of said areas,and the frequency channels rearranged by the channel mapping circuit areorthogonally multiplexed. Note that the rearrangement of channels in theabove described invention can be carried out with respect to paralleloutput signal sequences of an identical symbol rate, or paralleltransmission baseband signal sequences corresponding to a plurality ofusers.

According to such a present invention, the efficient utilization of thesystem band can be realized by rearranging the frequency channelsassigned with respect to each cell (base station) into continuousfrequency channels for each cell (base station), and compressing thisinto a narrow band by orthogonal multiplexing. Namely, by rearrangingthe frequency channels into a continuous system band, it becomespossible to omit the overhead due to the fact that the frequencychannels are discontinuous such as the guard interval, and it becomespossible to realize the efficient utilization of the resources. Also, byusing the parallel output signal sequences of the identical symbol rateand the baseband signal sequences as the target of the rearrangement,the compressibility can be raised, and it becomes possible to utilizethe resources more efficiently.

In the above described invention, it is preferable to acquire a searchtable indicating a using state of frequency channels used in nearbyareas and carry out a search of a vacant channel, and rearrange thefrequency channels according to this search result and assign continuouschannels with respect to identical cell. In this case, it becomespossible to integrally manage the frequency channels used in a pluralityof cells, the detection of the unused frequency channel becomes easier,and the speed up of the processing can be realized. Note that thissearch table may be managed by the base station control device, forexample, or the sharing of information can be realized by carrying outtransmission and reception of data between the radio devices andestablishing the synchronization.

It is preferable to carry out the rearrangement of the frequencychannels in the present invention, by searching whether or not a vacantfrequency channel exists within a band to be continuously secured withrespect to an arbitrary base station, according to the search table, and

(a) in the case where the vacant frequency channel exists within thisband to be continuously secured, changing the assignment to this basestation, and

(b) in the case where the vacant frequency channel does not exist withinthis band to be continuously secured, counting the vacant frequencychannels outside this band to be continuously secured, and when morethan or equal to a prescribed number of the vacant frequency channelsare secured, holding the information regarding these vacant frequencychannels in a vacancy memory table, and changing the frequency channelsof another base station used within the band to be continuously securedto the frequency channels held in the vacancy memory table, and

(c) repeating the processing of (a) and (b).

In this case, it is possible to make the assignment to an arbitrary cell(base station) according to the distribution of the used/unusedfrequency channels, by using the search table.

Note that, in the present invention, unused frequency channels aregenerated by repeating rearrangement of channels and the orthogonalmultiplexing, and new channels are assigned to generated unusedfrequency channels. In this case, it is possible to realize thediversity of the frequency channel assignment, such as assigning achannel of an arbitrary cell (base station) with respect to thefrequency channel which has newly become an unused state by thecompression.

In the present invention, in the case where this radio communicationsystem has a hierarchical cell structure formed by a macro-cell andmicro-cells contained in this macro-cell, and these macro-cell andmicro-cells use an identical frequency band, it is preferable to shift apartition which is a boundary between a frequency channel band of themacro-cell and a frequency channel band of the micro-cells, and thenconcentrate vacant channels before and after the partition by carryingout rearrangement of the frequency channels by searching vacantchannels, using a shifted partition as a reference. In this case, it ispreferable to carry out the shifting of the partition by giving apriority level for each frequency channel according to a traffic statein the macro-cell and micro-cells, and rearranging the frequencychannels according to this priority level. In this case, even in thesystem which forms the hierarchical cell structure, it becomes possibleto properly arrange and compress unused channels while carrying out theadjustment of the frequency band, between the upper level hierarchy andthe lower level hierarchy, by appropriately shifting the partition.

Note that, in the present invention, a transmission scheme used by thisradio communication system is preferably a scheme for spreading theinformation symbol in a plurality of time regions or frequency regions,according to a spread code assigned to a terminal of a receiving side,and making a rate of the spread code with respect to the informationsymbol rate variable.

In this case, the wide band system of the OFDM scheme and the narrowband system can coexist in the identical frequency band, so that the newgeneration communication scheme can coexist by using two schemes in thesame frequency band, and in the case of changing the communicationscheme, it is possible to make a smooth transition by stages from theprevious scheme to the new scheme.

Moreover, the present invention is such that, in a signal transmissionmethod for converting information data sequences into a plurality ofchannels, and transmitting and receiving a signal sequence of each ofthese plurality of channels by a plurality of orthogonalized sub-carriersignals, a propagation route of the sub-carrier signals is estimated,and a bandwidth of the sub-carrier signals to be transmitted andreceived, according to this estimated fading information. According tosuch a present invention, the bandwidth of the sub-carriers iscontrolled according to the state of the propagation route, so that itbecomes possible to efficiently utilize the maximum tolerable bandwidthaccording to the communication environment, and it is possible torealize the improvement of the communication quality and thetransmission characteristics.

In the present invention, it is preferable to calculate a requirednumber of sub-carriers that can be assigned to a user, according to thecontrolled sub-carrier bandwidth, and branch a number of the pluralityof sub-carriers to be transmitted and received into the required numberof sub-carriers. In this case, it is possible to use the appropriatenumber of sub-carriers according to the propagation environment and thenumber of users.

In the present invention, it is preferable to generate a fading timevariation information and a delay distortion information in a radio wavepropagation path, according to a waveform of received signals, andestimate the propagation route according to these information. In thiscase, the fading can be estimated by utilizing the radio waves receivedat the receiving side, so that it is possible to carry out the controlof the sub-carrier bandwidth at higher precision.

In the present invention, it is preferable to transmit the estimatedfading information by multiplexing it with a user data information, andseparate the fading information from a received data matrix. In thiscase, by transmitting the fading information acquired at the receivingside to the correspondent, it is possible to share the informationregarding the propagation environment at both sides of the transmittingside and the receiving side.

In the present invention, at the transmitting side, it is preferable tohave a step for detecting a sub-carrier bandwidth information accordingto the fading information and calculating a clock frequency from thedetected sub-carrier bandwidth information, a step for converting agenerated frequency into the calculated clock frequency and carrying outserial to parallel conversion at the clock frequency according to thissub-carrier frequency, and a step for selecting a desired channel from asingle or plurality of sub-carrier channels after an inverse discreteFourier transform. In this case, the it is possible to set the signalspeed according to the fading so that it is possible to carry out thetransmission of signals efficiently.

In the present invention, it is preferable to have a function forcalculating a total bandwidth to be assigned to this user from arequired information bit transmission speed of the user, and calculatingthe required number of sub-carriers from the total bandwidth and thesub-carrier bandwidth information. In this case, the required number ofsub-carriers with respect to the total bandwidth is calculated byaccounting for the actual communication power of the user, so that it ispossible to distribute the resources in well balanced manner accordingto the utilization state of the resources of the entire system, and itis possible to realize the dispersion of loads.

In the present invention, it is preferable to make a setting regardingan optimum sub-carrier bandwidth, a required number of sub-carriers, anda guard interval according to the fading information, at a time ofcommunication start. In this case, it is possible to set the guardinterval according to the sub-carrier bandwidth and the number ofsub-carriers that are set according to the state of the propagationroute, so that it is possible to realize the appropriate interferenceprevention.

Note that this setting of the guard interval length can be madeperiodically at a prescribed time interval determined in advance, or ina case where an optimum sub-carrier bandwidth, a required number ofsub-carriers, a guard interval, or a signal error rate becomes less thanor equal to a certain reference, besides at a time of the communicationstart.

In the present invention, a transmission scheme used by this radiocommunication system is preferably a scheme for spreading theinformation symbol in a plurality of time regions or frequency regions,according to a spread code assigned to a terminal of a receiving side,and making a rate of the spread code with respect to the informationsymbol rate variable.

In this case, the information symbol can be transmitted by dividing theinformation symbol on a plurality of frequency axes according to thepropagation route (fading) state, and spreading it by the spread code ofthe variable spreading rate assigned to each reception device, so thatit is possible to multiplex the signals of a plurality of users with thesignals of the identical time in the identical frequency band accordingto the propagation route of each reception device, and it is possible toprevent the interferences between the users while realizing theefficient utilization of the resources. As a result, the wide bandsystem of the OFDM scheme and the narrow band system can coexist in theidentical frequency band, so that the new generation communicationscheme can coexist by using two schemes in the same frequency band, andin the case of changing the communication scheme, it is possible to makea smooth transition by stages from the previous scheme to the newscheme.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure showing a power spectrum of a conventional generalfrequency division multiplexing scheme.

FIG. 2 is a figure showing a frequency interval of the sub-carriers in aconventional OFDM scheme.

FIG. 3 is a block diagram showing a configuration of a conventional OFDMradio device using an inverse discrete Fourier transform circuit.

FIG. 4 is a figure showing a spectrum of a conventional BDMA scheme.

FIG. 5 is a figure of a frequency channel band in a conventional OFDM.

FIG. 6 is a block diagram showing a structure of a conventionaltransmission device.

FIG. 7 is a figure showing an influence of the multi-path in the case ofattaching a guard band in a conventional transmission scheme.

FIG. 8 is a figure showing an influence of the Doppler shift in aconventional case.

FIG. 9 is a figure showing an influence due to a frequency selectivefading in a conventional case.

FIG. 10 is a figure showing an example of a frequency spectrum in aconventional case.

FIG. 11 is a block diagram showing a schematic configuration of a radiocommunication system of the present invention.

FIG. 12 is a figure showing a cell structure according to the first tofourth embodiments.

FIG. 13 is an explanatory figure showing an overall configuration of asystem according to the first to fourth embodiments.

FIG. 14 is a block diagram showing an internal configuration of a radiodevice according to the first embodiment.

FIG. 15 is a figure showing a configuration of a digital signalmodulation according to the first embodiment.

FIG. 16 is a figure showing a rearrangement of frequency channelsaccording to the first embodiment.

FIG. 17 is a figure showing a search table and a vacancy memory tableaccording to the first embodiment.

FIG. 18 is a block diagram showing an internal configuration of a radiodevice according to a modified embodiment of the first embodiment.

FIG. 19 is a flow chart showing an overall procedure for a channelassignment according to the first embodiment.

FIG. 20 is a flow chart showing in detail a procedure for a channelrearrangement according to the first embodiment.

FIG. 21 is a figure showing rearranged frequency channels in the firstembodiment.

FIG. 22 is a block diagram showing an internal configuration of a radiodevice according to the second embodiment.

FIG. 23 is a flow chart showing an overall procedure for a channelassignment according to the third embodiment.

FIG. 24 is a flow chart showing an overall procedure for a channelassignment according to the fourth embodiment.

FIG. 25 is a figure showing an overall configuration of a systemaccording to the fifth embodiment typically.

FIG. 26 is a figure showing a search table according to the fifthembodiment.

FIG. 27 is a flow chart showing a procedure for a partition shiftingcontrol in the fifth embodiment.

FIG. 28 is a flow chart showing a procedure for a channel assignmentaccording to the fifth embodiment.

FIG. 29 is a block diagram showing an internal configuration of a radiodevice according to the sixth embodiment.

FIG. 30 is a block diagram showing an internal configuration of atransmission device according to the seventh embodiment.

FIG. 31 is a block diagram showing in detail a configuration of a radiotransmitter provided at a transmission unit and a reception unitaccording to the seventh embodiment.

FIG. 32 is a block diagram showing an internal configuration of atransmission device according to the eighth embodiment.

FIG. 33 is a block diagram showing an internal configuration of atransmission device according to the ninth embodiment.

FIG. 34 is a figure showing an operation of a sub-carrier frequencychannel assignment in which a transmission band is variable, in achannel mapping according to the tenth embodiment.

FIG. 35 is a block diagram showing in detail an internal configurationof a channel mapping circuit in the eleventh embodiment.

FIG. 36 is a block diagram showing an internal configuration of atransmission device according to the twelfth embodiment.

FIG. 37 is a flow chart showing a procedure for setting a guard intervallength at a time of communication start in the twelfth embodiment.

FIG. 38 is a flow chart showing a procedure for periodically re-settingat each time of changing a frame in the twelfth embodiment.

FIG. 39 is a flow chart showing a procedure for periodically re-settingat each time of changing a frame in the twelfth embodiment.

FIG. 40 is a block diagram showing an internal configuration of atransmission device according to the thirteenth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the embodiments of the present invention will bedescribed by using the drawings.

FIG. 11 shows a schematic configuration of a radio communication systemaccording to the present invention. The radio communication system ofFIG. 11 comprises a channel mapping unit 501 and a bandwidth controlunit 502. In this radio communication system, the efficient utilizationof the frequency band is realized by introducing the OFDM scheme intothe frequency band which happens to have some vacancy, at the channelmapping unit 501, on an assumption that the respective frequency bandsutilized by the wide band system of the OFDM scheme and the narrow bandsystem (PDC=800 MHz, GSM, PHS, 3G system=2 GHz, radio LAN=2.4 GHz, etc.)are coexisting. The channel mapping unit 501 can assign new resources tothe system band by rearranging the frequency channels assigned to eachcell (base station) into continuous frequency channels for each cell(base station), and compressing them into a narrow band by orthogonallymultiplexing them. In addition, at the bandwidth control unit 502, thefurther improvement of the transmission characteristics is realized bycontrolling the sub-carrier bandwidth and the number of sub-carriersoptimally, by accounting for the fading variation at the receiving side.

In the following, the detail of the channel mapping unit 501 will bedescribed in detail in the first embodiment to the sixth embodiment, andthe detail of the bandwidth control unit 502 will be described in detailin the seventh embodiment to the thirteenth embodiment.

First Embodiment

(System Configuration)

The first embodiment of the present invention will be described. Notethat the present embodiment will be described for an exemplary case inwhich a plurality of cells R₁, R₂, R₃ . . . are such that, as shown inFIG. 12, radio communications are carried out by the frequency repeatingcell configuration with the cluster size of 7, and the frequencyarrangement numbers nc=#1, #2, #3, #4 . . . . . . . . . #nc . . . . . .. . . #700 are repeatedly assigned respectively to R1, R2, R3, . . . R7.

As shown in FIG. 13, in the communication system according to thepresent embodiment, the radio base stations 411, 421, 431 . . . forrespectively managing a plurality of cells R1, R2, R3 . . . and radiomobile stations 412, 422, 432 . . . located in respective cells carryout transmission and reception of signals through radio channels 413,423, 433. Then, each radio base station 411, 421, 431 is connected to acontrol station 405 through a channel 404, and made possible tocommunicate with the other communication systems through this controlstation 405.

FIG. 14 is a block diagram showing a configuration of a system accordingto the present embodiment. This system comprises a transmission unit 100and a reception unit 200, which is provided as a radio device for aradio base station, a radio mobile station, etc. Note that, thisembodiment will be described for an exemplary case in which thiscommunication system is provided at a radio mobile station.

As shown in FIG. 14, the transmission unit 100 has a serial to parallelconverter 111, into which data sequences a₁, a₂, . . . a_(y) destined torespective users are inputted, for converting these data sequences intoparallel signals, a frame formation circuit 118 for forming a frameaccording to the burst signal (synchronization signal), a symbol mapper112 for carrying out the baseband digital modulation, a channelselection device 113 for carrying out the channel assignment, a parallelto serial converter 114 for applying the parallel to serial conversionto the output signals from the channel selection device 113 andconverting them into time series transmission signals, and a radiotransmitter 115 for amplifying power after converting them into a radiofrequency band used by the system and transmitting them through atransmission antenna 116.

The serial to parallel converter 111 is a circuit for convertingarbitrary number of sub-carriers into a plurality of channels accordingto information indicated by the data to be transmitted, and in thepresent embodiment, it has a function for converting signals withdifferent symbol rates into a plurality of frequency channels with anidentical symbol rate.

The symbol mapper 112 carries out the modulation of the baseband digitalsignals, and in the present embodiment, it has a function fordemultiplexing the information frequency channel and the controlfrequency channel from the FDMA or TDMA signals. This digital signalmodulation has a function for discretely changing the amplitude, phaseand frequency of the carrier according to the multi-valued symbol andforming a constellation in a signal space diagram on the complex plane,and replaces them by the baseband signals of the I frequency channel andthe Q frequency channel of these modulated waves and generates themodulated waves, as shown in FIG. 14.

The frame formation circuit 118 is a circuit or converting the digitalsignals into the burst signals of the FDMA or TDMA signals, as shown inFIG. 15.

The channel selection device 113 has a channel mapping circuit 1131 forassigning the serial output signal sequences to the particularcontinuous channels of the system band, and an inverse discrete Fouriertransform circuit 1132 for applying the inverse Fourier transform to theoutput signals of said frequency channel mapping means and convertingthem into the plurality of orthogonalized sub-carrier frequency channelsignals.

The channel mapping circuit 1131 is a circuit for carrying out thecontinuous frequency channel assignment, and the inverse discreteFourier transform circuit 1132 is a circuit for carrying out thecompression of the occupied band by orthogonally multiplexing all thefrequency channels. In particular, in the case where the frequencychannels are continuously arranged, this inverse discrete Fouriertransform circuit 1132 has a function for converting them into thesub-carriers by orthogonally multiplexing this portion.

To describe in detail the signal assignment by the channel mappingcircuit 1131, as shown in FIG. 16(a), at the beginning, the arbitrarynumber of sub-carriers according to the user's requests are assigned tothe frequency channels of the respective cells R₁, R₂, R₃, . . . R₇.Then, at the transmission unit 100, when there are input (speech callorigination, packet transmission) of data a₁, a₂, . . . a_(y) from therespective users, via the serial to parallel converter 111 and the frameformation circuit 118, the modulation such as QPSK is carried out at thesymbol mapper 112. At this point, they are branched into a plurality offrequency channels by the required bit rate at the serial to parallelconverter 111, and the overall necessary number of frequency channels tobe assigned is determined. As the necessary bit rate is different foreach reception radio station 2, the number of frequency channels to beassigned is also different.

Also, at the serial to parallel converter 111, the required bit rate issecured at the radio channel assignment between the radio base stationand the radio mobile station. For example, when one channel of the basicfrequency channel has the bit rate B and the data sequence an from theuser has the bit rate of 3B, the assignment of 3 frequency channels iscarried out. The symbol mapper 112 carries out the modulation of thebaseband digital signals, and in the present embodiment, itdemultiplexes the information frequency channel and the controlfrequency channel from the FDMA or TDMA signals. More specifically, thisdigital signal modulation discretely changes the amplitude, phase andfrequency of the carrier according to the multi-valued symbol, forms aconstellation in a signal space diagram on the complex plane, replacesthem by the baseband signals of the I frequency channel and the Qfrequency channel of these modulated waves, and generates the modulatedwaves.

At the channel mapping circuit 1131, as shown in FIG. 16(b), therearrangement of the assignment of the frequency channels is carriedout, and for each area, the parallel output signal sequences in whichthe respective frequency channels have the identical symbol rate areassigned to particular continuous frequency channels of the system band.In addition, the channel mapping circuit 1131 orthogonally multiplexesthe respective re-assigned and mapped carrier frequencies at the inversediscrete Fourier transform circuit 1132, and converts them by theparallel to serial converter 114. In this orthogonal multiplexing, inthe case where the frequency channels are continuously arranged, thecompression of the occupied band is carried out by converting them intothe sub-carriers by orthogonally multiplexing this portion, as shown inFIG. 16(c).

Also, the channel mapping circuit 1131 has a function for acquiring thesearch table T1 as shown in FIG. 17 and referring it at a time ofcarrying out the rearrangement of the frequency arrangement. In thepresent embodiment, the search table T1 is a database maintained withinthe control station 405, which stores the arrangement number of thecommunication frequency channel, the belonging area, and the statedistinction as to whether it is vacant or used, for all the frequencychannels, and the information regarding all the frequency channels isshared at the respective radio base stations as this search table T1 isacquired by the channel mapping circuit 1131 of each radio base station.

In the present embodiment, assuming that the frequency arrangementnumber nc=#1, #2, #3, #4, . . . . . . . . . #nc . . . . . . . . . #700are repeatedly assigned to R1, R2, R3, . . . R7 respectively, the searchtable T1 has two transmission information of vac when the using state ofthe frequency channel is a vacant state and occ when it is a occupiedstate, for each cell. More specifically, denoting f(arrangement numberof frequency channel, belonging area, state distinction), the searchtable T1 stores f(1, 1, occ), f(2, 2, occ), f(3, 3, vac), f(4, 4, vac),f(5, 5, vac), f(6, 6, vac), f(7, 7, occ), f(8, 1, occ), f(9, 2, occ), .. . f(#nc, r, state).

Also, the search table T1 is made such that, as shown in FIG. 17, in thecase where the vacant frequency channel does not exist within the bandto be continuously secured at a time of referring the search table T1,the vacant frequency channels outside this band to be continuouslysecured are counted, and when more than or equal to a prescribed numberof the vacant frequency channels are secured, it cooperates with thevacancy memory table T2 for holding the information regarding thesevacant frequency channels. This vacancy memory table T2 holds theinformation regarding the counted vacant frequency channels which iscopied from the search table T1, and it is used at a time of changingthe frequency channels of another radio base station which are usedwithin a said band to be continuously secured to the frequency channelsheld in said vacancy memory table.

Note that, in the present embodiment, the search table T1 is storedwithin the control station 405, and the information is shared by aplurality of radio devices as the channel mapping circuit 1131 of eachdevice acquires it from the control station 405, but, for example, asshown in FIG. 18, the negotiation processing for realizing thesynchronization of the search table T1 may be carried out by thetransmission and reception of the search table T1 information betweenthe channel mapping circuits 1131 of the respective radio devices.Namely, the transmission units 100 of the radio base stations areconnected by the optical fiber network or the like and the informationregarding the latest frequency channel using state is always sharedbetween the neighboring radio base stations. Then, in the presentembodiment, each frequency channel is assigned in advance by each radiobase station to the unique frequency channel. The assignment control iscarried out autonomously and distributedly by utilizing the fact thateach radio base station shares the frequency channel information withthe surrounding cells.

On the other hand, as shown in FIG. 14, the reception unit 200 has aradio receiver 215, a serial to parallel converter 211, a discreteFourier transform circuit 213, a frame separation circuit 218, a symboljudgement unit 212, a parallel to serial converter 214, a channelformation circuit 217, and a reception antenna 216.

In such a reception unit 200, the signals transmitted from the otherdevice are received by the reception antenna 216, and the continuousdata signals converted into the baseband signals by the radio receiver215 are serial to parallel converted at the symbol time interval at theserial to parallel converter 211. Then, these output signals areextracted into a plurality of sub-carrier signal components at thediscrete Fourier transform circuit 213, and the extracted single orplurality of sub-carrier channel signals are separated for each frame atthe frame separation circuit 218, and this is baseband digitaldemodulated at the symbol judgement unit 212, and further they areserial to parallel converted to output the complex symbol sequences fordesired users at the parallel to serial converter 214, and after thechannels are formed by the channel formation circuit 217, they areoutputted as the data sequences a₁ to a_(x) destined to the respectiveusers.

(System Operation)

The processing procedure by the communication system according to thepresent embodiment is as follows. FIG. 19 is a flow chart showing thebasic processing procedure in the present embodiment.

First, when there are input (baseband signals of speech callorigination, packet transmission, etc.) of data a₁, a₂, . . . a_(y) fromthe users (S101), the inputted data a₁, a₂, . . . a_(y) are modulatedinto a plurality of frequency channels of the transmission speeddetermined in advance by the required bit rate at the speed converter117, and branched into the necessary number of the frequency channels tobe assigned (S102 and S103)

Next, the modulation such as QPSK is carried out and the symbol mapper112 and the information bit sequence is converted into the symbolsequence (S₀, S₁, S₂, S₃). Then, the modulated signals are assigned tothe continuous frequency channels at the channel mapping circuit 1131(S104), all the frequency channels are compressed by orthogonallymultiplexing them by the inverse discrete Fourier transform circuit 1132(S105), and after the frequency channels with large nc are arrangedcontinuously at the channel mapping circuit 1131 with respect to theband vacated by the compression (S106), they are transmitted by theradio transmitter 115 (S107).

In this way, by band compressing the continuous frequency channel bandby the orthogonal multiplexing and assigning the frequency channels withlarge nc to the vacated frequency band, and repeating this, it ispossible to collect the vacated high frequency band, assign the newfrequency channels of R₁ and utilize them for the frequency sharing orthe like with the other radio system.

Here, the processing at the steps S104 and S105 described above will bedescribed in detail. Here, the procedure for rearranging the continuousfrequency channels from nc=#1-#100 owned by each area, changing them tobe belonging to R₁, and band compressing them by the orthogonalmultiplexing will be described.

Describing it in detail, as shown in FIG. 21(a), the rearrangement ofthe frequency channels is carried out for the band for 100ch occupied bythe 100ch frequency channels, they are changed to be belonging to R₁,and they are compressed to the band for 50+1 (guard band part) ch by theorthogonal multiplexing. Namely, the band for 100−52==48 ch are vacated.The assignment of the frequency channels with large nc to this band iscarried out, and the unused bands are collected together to the highband and utilized for the other utilization purpose.

For this rearrangement processing, the procedure for securing 100 for ncby one procedure and band compressing by carrying out the rearrangementwill be described. FIG. 20 is a flow chart showing the procedure forband compressing.

At the search table T1, if there are vacant frequency channels innc=#1-#100, all of them are changed to r=1 and to be belonging to R₁(S202). Next, the vacant frequency channels of nc=#101-#700 are counted(S203), and when it is less than or equal to 86 (i>100−14), thecontinuous frequency channels cannot be secured by one procedure, sothat it returns to the step S202, and the processing for the next 100 isexecuted.

On the other hand, at the step S204, when i is greater than or equal to86, they are made to be belonging to (r=1), the vacant frequency channelnumber i sets of the vacancy memory tables T2 are prepared, and theinformation of the vacant frequency channels are copied from the searchtable T1 and held (S205).

Next, the vacant frequency channels are detected in an order of largernc in the search table T1, the switching of the frequency channelsassigned to those other than R₁ for nc=#1-#100 is carried out, and thecontents of the vacancy memory tables T2 are all copied to R₁ ofnc=#1-#100. At this point, the vacant frequency channels that match r=2are sequentially assigned in an order of larger one from the searchtable T1, for r=2 of nc=#1-#100 (f(2, 2, occ), f(9, 2, occ) . . . )(S206). BY such a switching, the vacated frequency channels are changedto r=1 and made to be belonging to the cell R₁. After that, thefrequency channel information used for the substitution is deleted fromthe vacancy memory tables T2. When there is no more frequency channelbelonging to r=2 of nc=#1-#100, the value of r is increased and thesimilar frequency channel switching is repeated for r=3, and this isrepeated up to r=7 (S206 to S209).

By the processing up to here, the changing to be belonging to r=1 forthe frequency channels nc=#1-#100 is completed, and the continuous 101frequency channels are secured (S210). Next, these bands are compressedby the orthogonal multiplexing (S211), the new channels are generated inthe band vacated by the compression, and they are assigned to the cellR₁ (S212).

More specifically, the band for 100ch occupied by 100ch frequencychannels is compressed to the band for 50+1 (guard band part) ch by theorthogonal multiplexing at the inverse discrete Fourier transformcircuit 1132, and the band for 100−51=49 ch is vacated. The assignmentof the frequency channels with large nc to this vacated band is carriedout, the unused bands are collected, and it becomes possible to utilizethem for the other utilization purpose.

(Effects)

According to such a communication system according to the presentembodiment, as shown in FIG. 21(a), for the continuous frequency channelportion, there is no need to provide the guard band between respectivechannels by the orthogonal multiplexing, so that the utilizationefficiency of the frequency band becomes very high. In addition, theabove described processing can use the fast Fourier transform, and theefficiency and the speed of the processing can be raised by this. Thefrequency utilization efficiency can be raised higher than the case ofthe independent multi-carrier transmission, by the orthogonalmultiplexing. In other words, it becomes possible to use the bandvacated by the compression for the new frequency channel assignment.

(Modification)

Note that the present invention can also be applied to the radio LANsystem using the OFDM scheme, such as the radio LAN system IEEE802.11a,for example. In this case, it is often used in each independent room andit can be treated as an isolated cell, so that there is no need to carryout the frequency arrangement by accounting for the inter-cellinterferences, and as shown in FIG. 21(b), when the system band is 100MHz, there are 4 channels of the frequency channels with the channelinterval of 20 MHz within the identical AP, and it is possible to selectthe vacant channel from these four channels and carry out theassignment.

Second Embodiment

Next, the second embodiment of the present invention will be described.FIG. 22 is a block diagram showing an internal configuration of atransmission unit of a communication system according to the presentembodiment. Note that the case where the communication system is a radiobase station of a cellular mobile communication scheme will be describedhere, but the it has the similar configuration in the other cases.

As shown in FIG. 22, the transmission unit 100 according to the presentembodiment has a speed converter 117 instead of the serial to parallelconverter 111 described above, and in addition, it has a variable bandfilter 119.

The serial to parallel converter 111 is a circuit for branching theinputted data a₁, a₂, . . . a_(y) into a plurality of frequency channelswith a transmission speed determined in advance according to therequired bit rate, and convert them into as many signal sequences as thenecessary number of frequency channels to be assigned. The variable bandfilter 119 is a circuit for selecting and extracting only a prescribedfrequency band, and the communication is carried out though the radiotransmitter 115 by using the channel that passed through this variableband filter 115.

According to such a present embodiment, even in the case where therequired information bit rate is different for each mobile communicationterminal and the number of sub-carriers to be assigned by the channelselection device 113 and their central frequency are different for eachradio mobile station, it is possible to avoid the neighboring channelinterferences to another radio mobile station transmission signalswithin the system band, by making the passing bandwidth variable by thevariable band filter 119 about the central frequency. The output of thisvariable band filter 119 is converted into the frequency band used bythe system, the power is amplified, and transmitted to the transmissionpath at the radio transmitter 115.

Third Embodiment

Next, the third embodiment of the present invention will be described.In the first embodiment described above, the case of improving thefrequency utilization efficiency at R₁ by compressing a part of thefrequency channels assigned to the area R₁ by the orthogonalmultiplexing has been described. In this third embodiment, the case ofcompressing the frequency channels of the area other than R₁ as well bythe orthogonalization in order to further raise the efficiency of theentire system will be described. FIG. 23 is a flow chart showing theprocessing procedure according to the third embodiment.

First, the frequency channel assignment capable of the appropriatefrequency repetitive use is carried out by the FCA (S301). After that,an arbitrary continuous band is secured. Note that, here, an example inwhich the frequency channels are partitioned into groups of 150ch each(bound=150) will be described, but by giving an arbitrary value tobound, it can be applied to the securing of an arbitrary continuousband.

Next, at the search table T1, nc=#1 is set as a top (#bound_head=#1),and nc=#150 is set as a tail (#bound_end=#150). Then, within the searchtable T1, if there are vacant ones in nc=#1 to #150, they are allchanged to r=x (initial value: r=1) and made to be belonging to Rx(initial value: R1) (S302).

The vacant frequency channels from the tail (#bound_end=#150) to #700are counted (i) (S303). When i is greater than or equal tobound-(quotient of bound divided by the class size 7) (here it is 14),as many vacancy memory tables T2 as the number i of the vacant frequencychannels are prepared, and the information of the vacant frequencychannels is copied from the search table T1. When i is less thanbound-(quotient of bound divided by the class size 7), it is repeateduntil the vacancy appears (S305).

Next, for the order of smaller r=y1xCr of #bound_head<nc<#bound_end (R=2f(2, 2, occ), f(9, 2, occ) . . . ), the vacant frequency channels thatmatch r=y are sequentially assigned in the order of larger one among thevacancy memory tables T2. The frequency channel vacated by the switchingis immediately changed to r=x and made to be belonging to Rx. In thecase where there is no more frequency channels belonging to r=y leftfrom the vacancy memory tables T2 despite of the fact that there arefrequency channels of r=y of #bound_head<nc<#bound_end still remaining,the remaining ones are left as they are and y is incremented, and thesimilar frequency channel switching is repeated for the next r=y (by r=3after r=2) (S306 and S307). In r=y, if there are frequency channels of#bound_head<nc<#bound_end still remaining, they are also left as theyare and the next frequency channel switching is carries out, and it isrepeatedly carried out up to r=7 (up to y=6 when x=7). The remainingfrequency channels which are not frequency channel switched aresequentially assigned in the order of larger vacancy memory tablearrangement number nc, regardless of r (S308 and S309).

For the continuous 100ch secured by this work, every time they aresecured (S310), they are compressed by the orthogonalization, and thenew channels are generated and assigned to the band vacated by thecompression. After the compression, the value of r=x is incremented, andthe procedure up to the compression is repeated for the next r=x (R=2).The work to assign the continuous 100ch and compress them by theorthogonalization is repeated up to r=7 (S313 and S314). Then, when theprocessing is carried out for all the cells, it is finished (S315).

As such, according to the present embodiment, the band for 100choccupied by the 100ch frequency channels are compressed to the band for51+1 (guard band part) ch by the orthogonal multiplexing, so that forthe system as a whole, the band for 48ch×7 cells are vacated. In thecase of 1ch=25 kHz, the continuous band of 8.4 MHz is vacated andsecured. The assignment of the frequency channels with large nc to thisvacant band is carried out, the unused bands are collected, and itbecomes possible to utilize them for the other utilization purpose.

Fourth Embodiment

Next, the fourth embodiment of the present invention will be described.In the first embodiment described above, the method for continuouslyarranging 100ch frequency channels to each area (R₁ to R₇) andcompressing them has been proposed. By compressing 100ch by theorthogonalization, the frequency band that has been occupied until thenand vacated is efficiently increased, but to secure the continuous bandfor 100ch is impossible except in the case where there are 100chvacancy, so that in the actually operated system (the call loss rateabout 3%), there is a possibility that it cannot be applied.

Also, even when an arbitrary value is given to bound, if the assignmentis carried out one by one for R₁ to R₇, it is difficult to obtain thesufficient effect when bound is small. For this reason, this fourthembodiment adopts an algorithm which uses 100ch vacant frequencychannels and repeats securing the continuous band for 10ch for each celland compressing them by the orthogonalization. FIG. 24 is a flow chartsowing the operation of the communication system according to thepresent embodiment. First, it starts when the frequency channelassignment capable of the appropriate frequency repetitive use iscarried out by the FCA. Here, the frequency channels are partitionedinto groups of 100ch each (bound=10) (S401). Note that, by giving anarbitrary value to bound, it can be applied to the securing of anarbitrary continuous band.

Next, nc=#1 is set as a top (#bound_head=#1), and nc=#10 is set as atail (#bound_end=#10). If there are vacant ones in nc=#1 to #10, theyare all changed to r=x (initial value: r=1) and made to be belonging toRx (initial value: R₁) (S402 and S403).

Next, the vacant frequency channels from the tail (#bound_end=#10) to#700 are counted (i) (S404). When i is greater than or equal tobound-(quotient of bound divided by the class size 7) (here it is 1), asmany vacancy memory tables T2 as the number i of the vacant frequencychannels are prepared, and the information of the vacant frequencychannels is copied from the search table (S405 and S406). On the otherhand, at the step S405, when i is less than bound-(quotient of bounddivided by the class size 7), the processing of the above describedsteps S403 to S405 is repeated until the vacancy appears.

For the order of smaller r=y₁xCr of #bound_head<nc<#bound_end (R=2 f(2,2, occ), f(9, 2, occ) . . . from), the vacant frequency channels thatmatch r=y are sequentially assigned in the order of larger one among thevacancy memory tables. The frequency channel vacated by the switching isimmediately changed to r=x and made to be belonging to Rx. In the casewhere there is no more frequency channels belonging to r=y left from thevacancy memory tables despite of the fact that there are frequencychannels of r=y of #bound_head<nc<#bound_end still remaining, theremaining ones are left as they are and y is incremented, and thesimilar frequency channel switching is repeated for the next r=y (by r=3after r=2).

In r=y, if there are frequency channels of #bound_head<nc<#bound_endstill remaining, they are also left as they are and the next frequencychannel switching is carries out, and it is repeatedly carried out up tor=7 (up to y=6 when x=7). The remaining frequency channels which are notfrequency channel switched are sequentially assigned in the order oflarger vacancy memory table arrangement number nc, regardless of r (S407to S410).

For the continuous 10ch secured by this work, every time they aresecured they are compressed by the orthogonalization (S411). After thecompression, the value of r=x is incremented, and the procedure up tothe compression is repeated for the next r=x (R=2). The work to assignthe continuous 10ch and compress them by the orthogonalization isrepeated up to r=7 (S412).

At this point, the comparison of the values of i and bound-int (bound/7)is made (S414), and when i is greater, the above described procedure ofthe compression by the orthogonalization is repeated. On the other hand,when i is less, it is finished.

By the above procedure, the band for 10ch occupied by the 10ch frequencychannels are compressed to the band for 5+1 (guard band part) ch by theorthogonal multiplexing, so that for the system as a whole, the band for3ch×7 cells×(number of repetition) are vacated. The assignment of thefrequency channels with large nc to this vacant band is carried out, theunused bands are collected, and it becomes possible to utilize them forthe other utilization purpose.

Fifth Embodiment

Next, the fifth embodiment of the present invention will be described.In the present embodiment, the frequency utilization efficiency isimproved similarly by the continuous band securing by the DSA and thecompression by the orthogonalization, similarly as FDMA and TDMA. Notethat, FIG. 25(a) is a figure showing a relationship of the macro-celland the micro-cells in the hierarchical cell typically, in the presentembodiment. Note that, in FIG. 25(a), the macro-cell and respectivemicro-cells are assumed to be sharing the identical frequency band.

Note that, in the present embodiment, in the case where the frequencychannels unique to each system are discontinuous by the measure againstthe macro-cell interferences, in order to carry out the frequencychannel arrangement aimed at the compression by the orthogonalization,to make the frequency channels transmitted from one radio base stationcontinuous on the frequency axis, the management of the frequencychannel assignment using the RP method for the continuous band securingis carried out. More specifically, as the method for assigning thefrequency channels between the hierarchical cells, the frequencychannels for use are separated for the macro-cell and the micro-cell,and a partition which is a border of these is controlled by thecommunication quality indicating the traffic state.

In the case of CDMA, the identical frequency repeating cell arrangementis theoretically possible, but in the case where a plurality ofmicro-cells which communicate by using the identical frequency bandexist within the macro-cell, the DSA becomes necessary as the measureagainst the identical frequency channel interferences. In the presentembodiment, the DSA function is provided at the base station controldevice, and the frequency efficient utilization is realized by this.This DSA is a system in which systems with different transmission speedscoexist, as in the micro-cell and the macro-cell of the identicalfrequency band, and when there is no more frequency channel on one side,the permission for use is given from one with the lower priority levelamong the vacant frequency channels on the other side.

More specifically, as shown in FIG. 25(a), the macro-cell M1 which is acommunication region of the macro-cell radio base station and themicro-cell M2 which is the communication region of the micro-cell radiobase station are hierarchically arranged in a form of overlapping. Inthese macro-cell M1 and micro-cell M2, the frequency channel assignmentis carried out in the identical frequency band. Each one of themicro-cells is set in relation to the macro-cell with the communicationregion which is overlapping with that micro-cell.

The radio communication network in the hierarchical cell structureaccording to the present embodiment is such that, as shown in FIG.25(b), the macro-cell exchanger X1 and the micro-cell exchanger X2 areconnected to the public communication network, and a plurality ofmacro-cell radio base stations BS1 and micro-cell radio base stationsBS2 are respectively connected to these exchangers. Each radio basestation BS1 and BS2 has a built-in control device formed by CPU andmemory, and stores the frequency channel search table T3 as shown inFIG. 26, and executes the frequency channel assignment and the controlof the partition autonomously. Note that the micro-cell radio basestation BS2 carries out the communication with the macro-cell radio basestation BS1 to which the own station belongs, and executes the frequencychannel assignment and the control of the partition autonomously.

The frequency channel search table T3 stores the frequency channelnumber and the vacant/occupied information for example for each area, asshown in FIG. 26. Note that the number of frequency channels stored inthe frequency channel search table T3 is 20 frequency channels, andamong them, the frequency channels of the frequency channel numbers 1 to7 are assigned to the macro-cell, and the frequency channels of thefrequency channel numbers 8 to 20 are assigned to the micro-cells.

(Partition Shifting Control)

FIG. 27 is a flow chart showing the processing procedure of thepartition shifting control. Note that this processing is executed by theprocessing device of the radio base station of each cell. Note that, inthe present embodiment, the partition is the border of the areas atwhich the frequency channels of the macro-cell and the micro-cell areseparated.

First, at the macro-cell radio base station, the call loss rate and theforced disconnection rate indicating the traffic state at the ownstation within the observation time T are measured (S501). Inconjunction with this, at the micro-cell radio base station, theoriginating call number, the call loss number and the forceddisconnection number within the observation time T at the own stationare measured (S508), and the measurement result is notified to thebelonging macro-cell radio base station (S509).

Next, at the macro-cell radio base station side, the measurement valuesat the step S508 are collected from the micro-cell radio base stations(S502), the call loss rate and the forced disconnection rate at all thebelonging micro-cells are calculated (S503), the communication qualitiesat both cells are calculated (S504), the calculation results arecompared, and the partition shift amount is calculated (S505), and thecalculation result which is the partition shift amount is notified tothe micro-cell radio base stations (S506), while the shifting of thepartition is executed (S507). On the other hand, at the micro-cell radiobase station side, the notice of the partition shift amount is receivedand the shifting of the partition of the own station is executed (S510and S511).

(Frequency Channel Assignment Procedure)

After the shifting of the partition is carried out in this way, theassignment of the frequency channels is carried out. Here, therearrangement (packing) of the frequency channels is carried out at atime of the frequency channel assignment at each cell, such that thefrequency channels changed from the macro-cell use to the micro-cell usecan be usable immediately at a time of the partition shifting. FIG. 28is a flow chart showing the processing procedure according to thepresent embodiment.

As shown in FIG. 28, when the packing is started (S601), first, thechannels of the partition position q and below (#7 and below shown inFIG. 26) are assigned to the macro-cell side (S602 to S603). Describingit in detail, the vacant channels are counted from the left side of thefrequency channel search table T3, and in the case where the vacantchannels of more than or equal to a prescribed number (which is 4 here)of ch are detected (S604 YES), the band compression by the orthogonalmultiplexing is carried out for that location (S605). In the case wherethe count number is i, it is compressed to i/2+1 (GB). The new channelsfor macro-cell are generated and assigned to the band vacated by thiscompression (S606).

Next, the channels of the partition position q and above (#8 and aboveshown in FIG. 26) are assigned to the micro-cell side (S607 to S608),Describing it in detail, the vacant channels are counted from the rightside of the frequency channel search table T3 up to the partitionposition, and in the case where the vacant channels of more than orequal to a prescribed number (which is 4 here) of ch are detected (S609YES), the band compression by the orthogonal multiplexing is carried outfor that location (S610). In the case where the count number is i, it iscompressed to i/2+1 (GB). The new channels for the micro-cell aregenerated and assigned to the band vacated by this compression (S611).

In this way, the assignment at the macro-cell is carried out accordingto the frequency channel search table T3, so that the macro-cell regionis in a state in which the order of being used at the micro-cell in thecase of carrying out the partition shifting is maintained even on thepartition left side. Also, after the packing, it becomes a state inwhich the frequency channels in use are arranged on the left side of themicro-cell search table. By carrying out the packing of the frequencychannels simultaneously with the channel release in this way, thefrequency channels assigned to the macro-cell near the partition have ahigh probability of being “vacant”, so that it becomes possible toutilize the frequency channels at the micro-cell immediately at a timeof the partition shifting, and it becomes possible to obtain the largercapacity.

Sixth Embodiment

Next, the sixth embodiment of the present invention will be described.In the present embodiment, an exemplary case where the rearrangement andthe compression by the multiplexing of the frequency channels in eachembodiment described above are applied to the variablespreading-orthogonal frequency code multiplexing (VSF-OFCDM: VariableSpreading Factor-Orthogonal Frequency Code Division Multiplexing)transmission scheme which is the fourth generation communication schemewill be described. In this VSF-OFCDM, the information symbol is dividedon a plurality of frequency axes, and the information symbol istransmitted by spreading it by a spread code of a variable spreadingrate which is assigned to each radio mobile station.

The transmission device according to the present modified embodimenthas, as shown in FIG. 29, at the transmission unit 100, a multiplexingunit 201 for multiplexing the transmission signals (information symbols)and the pilot signals, a serial/parallel conversion unit 202 forconverting the multiplexed signals into parallel signals, a copying unit230 for copying each signal sequence, a spread code generation unit 209for generating a spread code, a multiplication unit 204 for multiplyingeach signal sequence copied by the copying unit 203 with the spreadcode, a combining unit 205 for combining the multiplied signals, aninverse fast Fourier transform unit (IFFT) 206 for applying the inversefast Fourier transform to the combined signals, a parallel/serialconversion unit 207 for converting respective transformed signals into asingle signal sequence, a guard interval attaching unit 211, a data andcontrol signal combining circuit 219, a radio transmitter 115, and thechannel mapping circuit 1131 described above.

The serial/parallel conversion unit 202 is a circuit for converting theserial signals into parallel signals which are a plurality of signalsequences, according to the bandwidth and the number of sub-carrierscalculated by the transmission sub-carrier bandwidth control unit, andthe converted parallel signals are respectively outputted to the copyingunit 203.

The copying unit 203 is a circuit for copying each information symbol ofa plurality of information symbol sequences which are serial to parallelconverted at the serial/parallel conversion unit 202 as many as thenumber equal to the sequence length (chip length) of the spread code,and the copied information symbols are arranged on the frequency axisand outputted to the multiplication unit 204 as one set of theinformation symbol sequence.

The spread code generation unit 209 is a circuit for generating thespread code of a prescribed spreading rate which is assigned to eachradio mobile station as many as the number of sub-carriers, according tothe spreading rate inputted from the multiplexing control unit. Themultiplication unit 204 is a circuit for multiplying each informationsymbol copied at the copying unit 203 with the spread code generated bythe spread code generation unit 209.

The inverse fast Fourier transform unit 206 is a circuit for carryingout the inverse fast Fourier transform on a plurality of signalsequences inputted from the combining unit 205, according to thebandwidth and the number of sub-carriers calculated by the transmissionsub-carrier bandwidth control unit, and each transformed signal sequenceis outputted to the parallel/serial conversion unit 207.

The parallel/serial conversion unit 207 is a circuit for converting aplurality of signal sequences inputted from the inverse fast Fouriertransform unit 206 into serial signals which are a single signalsequence, according to the bandwidth and the number of sub-carrierscalculated by the transmission sub-carrier bandwidth control unit. Theguard interval attaching unit 221 inserts the guard interval into thesignals converted by the parallel/serial conversion unit 207.

The channel mapping circuit 1131 is the same as that of each embodimentdescribed above, which is a circuit for searching the continuousfrequency channels within the system band according to the search tableprovided at the control station 405, and carrying out the rearrangementof the frequency channels according to this search result.

Then, at the transmission unit 100, the data sequences rearranged by thechannel mapping circuit 1131 are multiplexed by the multiplexing unit201, and the multiplexed transmission signals are converted into theparallel signals formed by a plurality of signal sequences by theserial/parallel conversion unit (S/P) 202, and after carrying out thecopying processing at the copying unit 203, each signal sequence ismultiplied with the spread code generated by the spread code generationunit 209.

Next, after applying the inverse Fourier transform on these combinedsignals at the inverse fast Fourier transform unit (IFFT) 206, they areconverted into serial signals formed by a single signal sequence by theparallel/serial conversion unit (P/S) 207, the guard interval isinserted into these serial signals by the guard interval attaching unit221, each parameter calculated by the transmission sub-carrier bandwidthcontrol unit is combined by the data and control signal combiningcircuit 219, and the OFDM signals are transmitted.

On the other hand, as shown in FIG. 29, the transmission deviceaccording to the present embodiment has a radio receiver 215, a guardinterval removing unit 222, a serial/parallel conversion unit 301, afast Fourier transform unit 302, a channel estimation unit 307, a spreadcode generation unit 308, multiplication units 303 and 304, an adder305, and a parallel/serial conversion unit 306.

The serial/parallel conversion unit 301 is a circuit for converting theserial signals into parallel signals which are a plurality of signalsequences, according to the bandwidth and the number of sub-carrierscalculated by the received sub-carrier bandwidth control unit, and theconverted parallel signals are respectively outputted to the fastFourier transform unit 302. The parallel/serial conversion unit 306 is acircuit for converting a plurality of signal sequences inputted from theadder 305 into the serial signals which are a single signal sequence,according to the bandwidth and the number of sub-carriers calculated bythe received sub-carrier bandwidth control unit.

The channel estimation unit 307 is a circuit for extracting the pilotsignals from the signals transformed by the fast Fourier transform unit302, and estimating the channel variation value of each sub-carrieraccording to these pilot signals. Also, the multiplication units 303 and304 are circuits=for guaranteeing the variation of each sub-carrieraccording to the variation value estimated by the channel estimationunit 307 and multiplying the spread code generating by the spread codegeneration unit 308.

Then, at the reception unit 200, the guard interval is removed by theguard interval removing unit 222 from the received OFDM signals. Next,the data sequence from which the guard interval is removed is convertedinto parallel signals formed by a plurality of signal sequences by theserial/parallel conversion unit (S/P) 301, and the Fourier transform isapplied to each signal sequence at the fast Fourier transform unit (FFT)302. After that, each transformed signal is multiplied with thevariation value estimated by the channel estimation unit 307 and thespread code generated by the spread code generation unit, and they areconverted into the serial signals formed by a single signal sequence bythe parallel/serial conversion unit (P/S) 306, and these serial signalsare outputted as the demodulated signals.

According to such a transmission device according to the presentembodiment, the wide band system of the OFDM scheme and the narrow bandsystem can be made to coexist in the identical frequency band, so thatby using two schemes in the same frequency band together, the newgeneration communication scheme can be made to coexist, and in the caseof changing the communication scheme, a smooth transition in stages fromthe previous scheme to the new scheme can be made.

As described above, according to the radio communication system and theradio communication method of this invention, by enlarging the unusedchannels by rearranging the frequency channels in use and compressingthem by the orthogonal multiplexing, it is possible to utilize thefrequency channels in the band efficiently, in the various communicationschemes such as the digital cellular system, the orthogonal frequencydivision multiplexing scheme system CDMA scheme, etc.

Seventh Embodiment

(Configuration of the Transmission System)

The seventh embodiment of the radio communication system according tothe present invention will be described. FIG. 30 is a block diagramshowing an internal configuration of the transmission device used in theradio communication system according to the present embodiment. Notethat, in the present embodiment, an exemplary case of applying thetransmission device to the radio base station in the cellular mobilecommunication system will be described, but the present invention is notlimited to this, and can be applied to the other communication orbroadcasting system such as the digital broadcasting using the OFDMtransmission, for example.

As shown in FIG. 30, the transmission device according to the presentinvention is a device for carrying out the control to make thesub-carrier band of the downward channel data signals from the radiobase station variable according to the state of the propagation path,and more specifically, has a transmission unit 1100 for transmitting bythe orthogonal frequency division multiplexing modulation scheme and areception unit 1200 for enabling the acquisition of a fading (radio wavepropagation path) information from the downward channel.

(1) Configuration of the Transmission Unit

The transmission unit 1100 has a symbol mapper 1, a serial to parallelconverter 2, a channel mapping circuit 3, an inverse discrete Fouriertransform circuit 4, a parallel to serial converter 5, a radiotransmitter 6, a transmission antenna 7, a fading estimation unit 8, anda transmission sub-carrier bandwidth control unit 9.

The symbol mapper 1 is a module for carrying out the digital modulationwhen there is an input (speech call origination, packet transmission) ofdata from some user. Here, when the inputted data is a, the digitalmodulation such as QPSK, QAM, etc., for example is carried out for thisinputted data a at the symbol mapper 1. By this digital modulation, theinformation bit sequence is converted into a complex symbol sequenceS_(x) (S₀, S₁, S₂, S₃).

The serial to parallel converter 2 is a module for branching the complexsymbol sequence S_(x) (S₀, S₁, S₂, S₃) into a plurality of channels. Atthis point, the number of channels to be branched (which is assumed tobe M here) is determined by the transmission sub-carrier bandwidthcontrol unit 9.

In the present embodiment, the fading information for determining thesub-carrier width optimum for the downward channel is extracted from theupward channel by the radio receiver 11. Namely, the control forbranching into a plurality of channels (C₁, C₂, . . . C_(M)) at thetransmission sub-carrier bandwidth control unit 9 is such that thewaveform information is taken out from the received signals received atthe radio receiver 11 of the reception unit 1200, the fading informationin the upward channel is sent to the fading estimation unit 8, thesub-carrier bandwidth of the downward channel which has little influenceof the fading is calculated according to this fading information, andthe clock frequency conversion is carried out such that it becomes thisbandwidth.

Note that, the downward channel transmitted by the transmission deviceand the upward channel to obtain the information here are in many casesdifferent in the frequency division. The fading has its cause in thepropagation distance and the frequency of the radio base station and theradio mobile station, and the upward and downward channel frequencydivision in the cellular communication such as PDC is less than or equalto 130 MHz, so that the difference in the influence of the fading issmall.

In the present embodiment, from the fading information of the upwardchannel, at the fading estimation unit 8, the optimum sub-carrierbandwidth Bs is determined according to (1) the fading time variationinformation and (2) the delay distortion information. Then, at thetransmission sub-carrier bandwidth control unit 9, the clock oscillationfrequency for outputting this optimum sub-carrier bandwidth Bs is set asfck. Describing it in detail, at the transmission sub-carrier bandwidthcontrol unit 9, the control to generate the clock oscillation frequencyfck such that the bandwidth of each sub-carrier becomes Bs is carriedout, and this clock frequency fck information is sent respectively tothe serial to parallel converter 2, the channel mapping circuit 3, theinverse discrete Fourier transform circuit 4, and the parallel to serialconverter 5. The conversion for carrying out each orthogonal frequencydivision multiplexing transmission is carried out, and it istransmitted.

Here, the control information regarding the optimum sub-carrierbandwidth will be described in detail. As shown in FIG. 30, from thereceived signal waveform extracted from the radio receiver 11, at thefading estimation unit 8, the fading time variation information and thewaveform distortion information are calculated, and from this fadinginformation, at the transmission sub-carrier bandwidth control unit 9,the optimum sub-carrier width is determined, and the clock frequency fckinformation is sent to the serial to parallel converter 2, the channelmapping circuit 3, the inverse discrete Fourier transform circuit 4, andthe parallel to serial converter 5.

Also, at the receiving side, this sub-carrier bandwidth controlinformation for carrying out each conversion operation in thissub-carrier bandwidth is sent from the transmission sub-carrierbandwidth control unit 9 to the data and control signal combiningcircuit 19. At the data and control signal combining circuit 19, theinformation data sent from the parallel to serial converter 5 and thissub-carrier bandwidth control information sent from the transmissionsub-carrier bandwidth control unit 9 are combined, and simultaneouslytransmitted to the receiving side.

FIG. 31 is a block diagram showing in detail a configuration of theradio transmitter 6 provided in the transmission unit 1100. As shown inFIG. 31, the radio transmitter 6 comprises an LPF 61, an orthogonalmodulator 62, a frequency converter 63, and a transmission poweramplifier 64.

In order to transmit the baseband continuous signals outputted from theparallel to serial converter 5 and the optimum sub-carrier band controlinformation connected from the transmission sub-carrier bandwidthcontrol unit 9 simultaneously at the downward channel, these signals arefilter processed by the LPF 61 through the data and control signalcombining circuit 19, converted into the intermediate frequency by theorthogonal modulator 62, and converted into the RF frequency band usedin the system by the frequency converter 63, and the amplification forthe purpose of the transmission is carried out by the transmission poweramplifier 64.

(2) Configuration of the Reception Unit 1200

On the other hand, the reception unit 1200 has, as shown in FIG. 30, areception antenna 10, a radio receiver 11, a received sub-carrierbandwidth control unit 13, a serial to parallel converter 14, a discreteFourier transform circuit 15, a channel selection unit 16, a parallel toserial converter 17, and a symbol judgement 18.

In such a reception unit 1200, the signals transmitted from the otherdevice are received at the reception antenna 10, and the continuous datasignals converted into the baseband signals at the radio receiver 11 areserial to parallel converted at the symbol time interval at the serialto parallel converter 14.

Here, a plurality of sub-carrier signal components are extracted fromthese output signals at the discrete Fourier transform circuit 15. Atthis point, they are branched into all frequency channels (F₁, F₂, F₃, .. . F_(N)) of as many as the maximum sub-carrier number N in the case ofusing the conceivably narrowest band sub-carriers, but the channels bywhich the information data are actually conveyed are channels of a partof the all channels, so that by the channel selection means 16 forselectively outputting only a group of channels containing theinformation destined to the own station, only a group of channels (C₁,C₂, C₃, . . . C_(M)) containing the information are selected. In otherwords, N is a value less than or equal to M, and usually M=N/2, N/3, N/4. . . etc., which is determined by the Bs width. A single or pluralityof sub-carrier channel signals which are the output are serial toparallel converted to output the complex symbol sequence with respect toa desired user by the parallel to serial converter 17, and basebanddigital demodulated at the symbol judgement 18.

FIG. 31 is a block diagram showing an exemplary configuration of theradio receiver 11 provided in the reception unit 1200. As shown in FIG.31, the radio receiver 11 comprises a reception power amplifier 1111, afrequency converter 1112, an LPF 1113, and a detector 1114. At thereception power amplifier 1111, the signals with the level dropped dueto the fading are amplified, and converted from the RF frequency to theIF frequency by the frequency converter 1112.

These data are filtered by the LPF 1113, and converted into the basebandfrequency at the detector 1114. Then, the baseband continuous signalstransmitted by the upward channel and the optimum sub-carrier bandcontrol information connected from the transmission sub-carrierbandwidth control unit 9 that is transmitted simultaneously by theupward channel are separated, and the baseband continuous signals aresent to the serial to parallel converter 14, the optimum sub-carrierband control information is sent to the fading estimation unit 8, andthe fading information is sent to the transmission unit 1100.

(Effects)

According to such a transmission device according to the seventhembodiment, the fading at the upward channel is estimated from thesignals received at the upward channel, and the sub-carrier bandwidth atthe downward channel is controlled according to this estimation result,so that the improvement of the transmission characteristics can berealized.

Eighth Embodiment

Next, the eighth embodiment of the present invention will be described.FIG. 32 is a block diagram showing an internal configuration of thetransmission device according to the present embodiment. The presentembodiment has the feature that the fading estimation unit 8 in theseventh embodiment described above is provided with a Doppler shiftestimation and a delay profile estimation function. Note that, in FIG.32, in the transmission device according to the seventh embodimentdescribed above, a portion related to the Doppler shift estimation and adelay profile estimation function is mainly shown.

Namely, similarly as in the seventh embodiment, the transmission devicehas the transmission unit 110 formed by the symbol mapper 1, the serialto parallel converter 2, the channel mapping circuit 3, the inversediscrete Fourier transform circuit 4, the parallel to serial converter5, the radio transmitter 6, the transmission antenna 7, the fadingestimation unit 8 and the transmission sub-carrier bandwidth controlunit 9, and the reception unit 1200 formed by the reception antenna 10,the radio receiver 9, the sub-carrier band information extraction means12, the received sub-carrier bandwidth control means 13, the serial toparallel converter 14, the discrete Fourier transform circuit 15, thechannel selection means 16, the parallel to serial conversion means 17,and the symbol judgement 18.

Then, in particular, the fading estimation unit 8 according to thepresent embodiment has a control signal extraction unit 81 forextracting control signals from the received signals received by theradio receiver 9, a Doppler shift estimation unit 82 for estimating theDoppler shift according to the extracted control signals, and a delayprofile estimation unit 83 for estimating a delay profile according tothe control signals.

(Handling of the Fading Information)

The band variable processing operation of the transmitting side in thepresent embodiment will be described. Within the fading estimation unit8, the sub-carrier widest band Bs_w information obtained from the delayprofile estimation unit 83 and the sub-carrier narrowest band Bs_ninformation obtained from the Doppler shift estimation unit 82 arerespectively sent to the transmission sub-carrier bandwidth control unit9, and at the transmission sub-carrier bandwidth control unit 9, theinformation transmission bit rate Bs per sub-carrier which hardlyreceives the fading is determined. This information transmission bitrate information is sent to the data and control signal combiningcircuit 19.

As the method for calculating the sub-carrier band from the fadinginformation, the following examples are noted.

The Doppler shift f_(D) is obtained by the following formula from theaverage fade duration.$f_{D} = {\frac{1}{\sqrt{2\pi\quad\tau}}\frac{\sqrt{2b_{\theta}}}{R_{s}}\left( {{\exp\left( \frac{{Rs}^{2}}{2b_{\theta}} \right)} - 1} \right)}$

Note that, in the above formula, τ is the average fade duration, b₀ isthe average reception power, Rs is the regulation level.

Then, when the transmission frequency is 900 MHz, the moving speed v is50 km/h, the Doppler frequency f_(D) with respect to the average fadeduration for the level lower by 20 dB than the reception powercorresponds to 45.5 Hz.

It is known that the orthogonalized transmission is possible if themaximum Doppler frequency f_(D) falls within approximately 10% of theoccupied band Bs. Consequently, there is a need for the occupied band Bsto be the band of 455 Hz or more.

Also, the delay spread S is expressed as the standard deviation of thepower density function P(τ), and obtained from the following formula.$S = \sqrt{{\frac{1}{P_{m}}{\int_{\theta}^{3}{\tau^{2}{P(\tau)}{\mathbb{d}\tau}}}} - T_{D}^{2}}$

Note that, in the above formula, Pm is the reception power, τ is thedelay time, and T_(D) is the average delay.

Then, the correlation bandwidth Bc is obtained from the delay spread Sby the following formula. $B_{c} = \frac{1}{2\pi\quad S}$

In other words, in the case where the sub-carrier frequency band isnarrower than this correlation bandwidth Bc, the influence of the delayprofile will not be received. The sub-carrier clock oscillationfrequency fck is determined according to such an information, and thebandwidth per sub-carrier is obtained, and this is sent to the data andcontrol signal combining circuit 19 as the control information.

Note that, in the present embodiment, the guard interval Tg is set suchthat it becomes less than or equal to the maximum delay time τ.

Ninth Embodiment

Next, the ninth embodiment of the present invention will be described.FIG. 33 is a block diagram showing an internal configuration of thetransmission device according to the present embodiment. The presentembodiment has the feature that the transmission sub-carrier bandwidthcontrol unit 9 in the seventh embodiment and the eighth embodimentdescribed above is provided with a function for controlling thesub-carrier band variably by controlling the clock rate. Note that, inFIG. 33, in the transmission device according to the seventh embodimentand the eighth embodiment described above, a portion related to thesub-carrier band variable control function is mainly shown.

Namely, similarly as in the seventh embodiment and the eighthembodiment, the transmission device has the transmission unit 110 formedby the symbol mapper 1, the serial to parallel converter 2, the channelmapping circuit 3, the inverse discrete Fourier transform circuit 4, theparallel to serial converter 5, the radio transmitter 6, thetransmission antenna 7, the fading estimation unit 8 and thetransmission sub-carrier bandwidth control unit 9, and the receptionunit 1200 formed by the reception antenna 10, the radio receiver 9, thesub-carrier band information extraction means 12, the receivedsub-carrier bandwidth control means 13, the serial to parallel converter14, the discrete Fourier transform circuit 15, the channel selectionmeans 16, the parallel to serial conversion means 17, and the symboljudgement 18.

Then, in particular, in the present embodiment, the transmissionsub-carrier bandwidth control unit 9 has a clock rate converter 91, aclock oscillator 92, a clock control unit 93, and an optimum sub-carrierbandwidth calculation unit 94.

(Sub-Carrier Band Variable Control)

In the present embodiment, at the transmission sub-carrier bandwidthcontrol unit 9 of the transmission unit 1100, according to the fadinginformation given from the fading estimation unit 8, the optimumsub-carrier bandwidth Bs is calculated at the optimum sub-carrierbandwidth calculation unit 94.

Describing it in detail, the clock frequency to be a reference in orderto change it to the optimum sub-carrier occupied bandwidth Bs isconverted at the clock control unit 93. Namely, the clock rate CK Ratefor deriving Bs is determined at the clock control unit 93, and thefrequency conversion control command using this CK Rate is outputted tothe clock rate converter 91.

Note that, in the present embodiment, it is converted from the clockfrequency fcc generated by the clock oscillator 92 to the clock carrierfrequency fck by default. For example, it is fck=fcc/2, fcc/3, . . . orfck=2*fcc, 3*fcc, . . . etc. The clock output terminal of the clock rateconverter 91 is connected to the respective clock terminals of theserial to parallel converter 2, the channel mapping circuit 3, theinverse discrete Fourier transform circuit 4, and the parallel to serialconverter 5, and outputs the information for the control of eachportion. In addition, for the sake of the serial to parallel conversionat a time of receiving, this clock rate information is combined with thedata signals as the Bs control signal at the data and control signalcombining circuit 19, and transmitted to the receiving side.

Tenth Embodiment

Next, the tenth embodiment of the present invention will be described.The present embodiment has the feature that the channel mapping circuit3 in the ninth embodiment described above is provided with a sub-carrierfrequency channel assignment function which makes the transmission bandvariable. FIG. 34 shows the operation of the sub-carrier frequencychannel assignment which makes the transmission band variable, in thechannel mapping according to the present embodiment.

As shown in FIG. 34(a), the channel mapping circuit 3 according to thepresent embodiment has a mapping unit 31 for executing the channelmapping, and a required sub-carrier number control unit 32 forcontrolling the required number of sub-carriers of the mapping unit 31according to the fading information.

The mapping unit 31 assigns sub-carrier channels (C₁, C₂, C₃, . . .C_(M)) as many as to be assigned to a desired user to a group ofcontinuous sub-carrier channels (F₁, F₂, F₃, . . . F_(N)) which areadjacent within the Freq band, by using the required sub-carrier numberN control information from the required sub-carrier number control unit32. Also, with respect to the sub-carrier frequency channels not to besent which are distributed outside the Freq band, the mapping unit 31has a zero insertion circuit function for connecting to the ground whichsets the outputs of the corresponding sub-carrier frequency channels to0.

(Channel Mapping)

Then, in the present embodiment, as shown in FIG. 34(b), it is set asthe necessary occupied band Freq of a desired user, and at the channelmapping circuit 3, the sub-carrier channels (C₁, C₂, C₃, . . . C_(M)) asmany as to be assigned to a desired user are assigned to a group ofcontinuous sub-carrier channels (F₁, F₂, F₃, . . . F_(N)) which areadjacent within the Freq band, by using the required sub-carrier numberN control information from the required sub-carrier number control unit32. Also, the sub-carrier frequency channels not to be sent which aredistributed outside the Freq band are connected to the ground which setsthe outputs of the corresponding sub-carrier frequency channels(F_(M+1), . . . F_(N)) to 0.

Then, all frequency channels (F₁, F₂, F₃, . . . F_(N)) including theparallel output signals (C₁, C₂, C₃, . . . C_(M)) after the mapping areconverted into the time series transmission signals by the inversediscrete Fourier transform circuit 4, similarly as the embodimentsdescribed above.

Eleventh Embodiment

Next, the eleventh embodiment of the present invention will bedescribed. The present embodiment has the feature that the channelmapping circuit 3 in the tenth embodiment described above is providedwith a required sub-carrier number calculation means 31 and a userrequired information bit rate estimation unit 32, as shown in FIG. 35.

The user required information bit rate calculation unit 32 is a modulefor calculating the required information bit transmission speed a of theuser, according to the inputted data, and the required sub-carriercontrol unit 32 is a module for calculating the total bandwidth Banecessary for the user according to the required information bittransmission speed a of the user, and dividing it in units of theoptimum sub-carrier bandwidth Bs.

Then, in the case where the required sub-carrier control unit 32 and theuser required information bit rate calculation unit 32 calculate thetotal bandwidth Ba necessary for this user from the required informationbit transmission speed a of the user and divide it in units of theoptimum sub-carrier bandwidth Bs, the channel mapping circuit 3 carriesout the assignment of the frequency channels corresponding to therequired sub-carrier number Ns, according to the required sub-carriernumber Ns (=Ba/Bs) information to be used by the user which becomesnecessary.

Note that the required sub-carrier number to be used by the user canalso be obtained as Nsystem (=Bsystem/Bs) information, according to thecharacteristics of the system. In this case, the channel mapping circuit3 carries out the assignment of the frequency channel corresponding tothe required sub-carrier number Nsystem.

Twelfth Embodiment

Next, the twelfth embodiment of the present invention will be described.

(Configuration of the Transmission Device)

FIG. 36 is a block diagram showing an internal configuration of thetransmission device according to the present embodiment. As shown inFIG. 36, the transmission device according to the present invention alsocomprises the transmission unit 1100 and the reception unit 1200,similarly as in the above described embodiments.

(1) Transmission Unit

As shown in FIG. 36, the transmission unit 1100 has the symbol mapper 1,the serial to parallel converter 2, the channel mapping circuit 3, theinverse discrete Fourier transform circuit 4, the parallel to serialconverter 5′, the radio transmitter 6, the transmission antenna 7, thefading estimation unit 8, and the transmission sub-carrier bandwidthcontrol unit 9. Then, in particular, the transmission 1100 in thepresent embodiment has a guard interval attaching unit 21 for removingan influence of a delay distortion by attaching a guard interval, and aGI length control unit 23 for calculating an optimum guard intervallength regarding the OFDM according to the delay profile extracted atthe fading estimation unit 8.

Then, in the transmission unit 1100 of such a configuration, theinfluence of the delay distortion is removed by attaching the guardinterval at the guard interval attaching unit 21 to the baseband OFDMsignals multiplexed by the parallel to serial converter 5. At thispoint, as the guard interval length, the optimum guard interval lengthcalculated by the GI length control unit 23 according to the delayprofile extracted at the fading estimation unit 8 is used.

Namely, in the case where the multi-path having the delay spread longerthan the guard band length exists and the degradation of thecharacteristics becomes extremely large, compared with the case of notattaching the guard interval, the transmission speed of the data islowered as it becomes 1/(1+f₀Tg).

For this reason, in the present embodiment, the optimum guard intervalwidth of the minimum length for maintaining the sufficient length fornot receiving the influence due to the delay and improving the frequencyutilization efficiency is calculated from the delay profile extractedfrom the fading information and attached.

(2) Reception Unit

On the other hand, the reception unit 1200 has the reception antenna 10,the radio receiver 11, the fading estimation unit 8, the transmissionsub-carrier bandwidth control unit 9, the sub-carrier band informationextraction unit 12, the received sub-carrier bandwidth control unit 13,the serial to parallel converter 14, the discrete Fourier transformcircuit 15, the channel selection unit 16, the parallel to serialconverter 17, the symbol judgement 18, and the guard interval attachingunit 21.

The reception unit of the transmission device of the orthogonalfrequency division multiplexing modulation scheme will be described inFIG. 36. It has the reception unit 1200 comprising the reception antenna10, the radio receiver 11, the sub-carrier band information extractionunit 12, the received sub-carrier bandwidth control unit 13, the serialto parallel converter 14, the discrete Fourier transform circuit 15, thechannel selection unit 16, the parallel to serial converter 17, thesymbol judgement 18, and the guard interval removing unit 22.

The signals transmitted from the reception device of the orthogonalfrequency division multiplexing modulation scheme are received at thereception antenna 10, and the control signals are separated from thecontinuous data signals converted into the baseband signals at the radioreceiver 11. In each case of (1) at a time of communication start, (2)periodically, or (3) at a time of exceeding the error rate level, thereceived signal waveform is sent to the fading estimation unit 8.According to the fading information, the continuous data signals areserial to parallel converted at the symbol time interval at the serialto parallel converter 14. Here, Here, a plurality of sub-carrier signalcomponents are extracted from these output signals at the discreteFourier transform circuit 15. At this point, they are branched into allfrequency channels (F₁, F₂, F₃, . . . F_(N)) of as many as the maximumsub-carrier number N in the case of using the conceivably narrowest bandsub-carriers, but the channels by which the information data areactually conveyed are channels of a part of the all channels, so that bythe channel selection means 16 for selectively outputting only a groupof channels containing the information destined to the own station, onlya group of channels (C₁, C₂, C₃, . . . C_(M)) containing the informationare selected. In other words, N is a value less than or equal to M, andusually M=N/2, N/3, N/4 . . . etc. (It is determined according to the Bswidth.) A single or plurality of sub-carrier channel signals which arethe output are serial to parallel converted to output the complex symbolsequence with respect to a desired user by the parallel to serialconverter 17, and baseband digital demodulated at the symbol judgement18.

(Guard Interval Control)

As a timing for changing the guard interval, it is possible to adopt themethods of (1) to (3) enumerated in the following.

(1) At a Time of Communication Start

At a time of communication start, the delay profile is obtained from thereceived signal waveform at the fading estimation unit 8, and the guardinterval larger than the maximum delay time is set at the OFDM GI lengthcontrol unit 23. From the optimum guard interval length information sethere, the optimum guard interval is attached at the guard intervalattaching unit 21.

Such a method for setting at a time of communication start will bedescribed by using the flow chart of FIG. 37. First, at a time ofcommunication start, the fading information is extracted from thereceived signal waveform (the received waveform of the training signalportion, for example), and the delay profile and the maximum Dopplerfrequency are calculated (S701). Next, the required sub-carrier numberNs, the optimum sub-carrier bandwidth Bs, and the optimum guard intervallength TG are calculated (S702).

According to the information calculated at these steps S701 and S702,the inputted data are branched into channels of the required sub-carriernumber and the optimum sub-carrier bandwidth after the digitalmodulation (S703), the OFDM modulation is carried out by using therequired sub-carrier number Ns and the optimum sub-carrier bandwidth Bsthat are set (S704), and the guard interval of the optimum guardinterval length TG is attached to the baseband OFDM signals andtransmitted (S705). The setting of the parameters on the transmittingside is constant until a time of the communication end.

Then, by utilizing the data channel or the control channel, theinformation regarding each setting parameter is sent to the receivingside, and shared between it and the receiving side device (S706). Then,during a time until the communication end, the above described stepsS703 to S706 are repeated by the loop processing (S707).

(2) Periodical

Periodically, at every time of the frame change, such as a top or a lastof the frame, the delay profile is obtained from the received signalwaveform at the fading estimation unit 8, and the guard interval largerthan the maximum delay time is set at the OFDM GI length control unit23. From the optimum guard interval length information set here, theoptimum guard interval is attached at the guard interval attaching unit21.

Such a method for re-setting periodically, at every time of the framechange, such as a top or a last of the frame, will be described by usingthe flow chart of FIG. 38.

First, the received frame is monitored, and the frame change such as atop or a last of the frame is periodically detected (S801). Then, in thecase where the frame change is detected, the fading information isextracted from the signal waveform of the receiving side, the delayprofile and the maximum Doppler frequency are calculated (S802), and therequired sub-carrier number Ns, the optimum sub-carrier bandwidth Bs,and the optimum guard interval length TG are calculated (S803).

Next, according to these information, the inputted data are branchedinto channels of the required sub-carrier number Ns and the optimumsub-carrier bandwidth Bs after the digital modulation (S804), the OFDMmodulation is carried out by using the required sub-carrier number Nsand the optimum sub-carrier bandwidth Bs that are set (S805), and theguard interval of the optimum guard interval length TG is attached tothe baseband OFDM signals and transmitted (S806).

On the other hand, in the case where the frame change is not detected atthe step S801, without executing the above described steps S802 andS803, the channels are branched by using the input data by using therequired sub-carrier number Ns, the optimum sub-carrier bandwidth Bs,and the optimum guard interval length T_(G) that are already set (S804),and the OFDM modulation and the OFDM transmission are carried out (S805,S806).

Then, after the step S806, by utilizing the data channel or the controlchannel, the information regarding each setting parameter is sent to thereceiving side, and shared between it and the receiving side device(S807). Then, during a time until the communication end, the abovedescribed steps S801 to S807 are repeated by the loop processing (S808).

(3) At a Time of Exceeding the Error Rate Level

When the error rate judgement such as the CRC check, etc. is carried outduring the communication at the receiving side, the guard interval isre-set in the case where the detected error rate is larger than acertain constant level.

More specifically, the delay profile is obtained from the receivedsignal waveform at the fading estimation unit 8, and the guard intervallarger than the maximum delay time is set at the OFDM GI length controlunit 23. From the optimum guard interval length information set here,the optimum guard interval is attached at the guard interval attachingunit 21.

Such a method for re-setting the OFDM parameters when the error rateexceeds a certain constant level in the case where the error ratejudgement is carried out at the receiving side will be described byusing the flow chart of FIG. 39.

When the error rate judgement such as the CRC check is carried outduring the communication at the receiving side, the fading estimationunit 8 is operated in the case where the detected error rate is largerthan a certain constant level, and the fading information such as thedelay profile and the maximum Doppler frequency, for example, isextracted from the received signal waveform (S901).

Next, using these fading information, the required sub-carrier numberNs, the optimum sub-carrier bandwidth Bs, and the optimum guard intervallength T_(G) are calculated (S902). According to these information, theinputted data are branched into channels of the required sub-carriernumber Ns after the digital modulation (S903), the OFDM modulation intothe optimum sub-carrier bandwidth is carried out (S904), and the optimumguard interval length T_(G) is attached to the baseband OFDM signals andtransmitted (S905). After that, by utilizing the data channel or thecontrol channel, the information regarding each setting parameter issent to the receiving side, and shared between it and the receiving sidedevice (S906).

As for the guard interval length, a command for shortening the guardinterval gradually (T_(G)=T_(G)+ΔT_(G)) is sent to the transmittingside, when the communication quality is good as the error rate does notrise for times greater than or equal to a certain constant number ofrepeat times (N_(α) times) at the receiving side. Namely, afterexecuting the processing of the above described steps S901 to S906, thedetection of the frame error rate is carried out by the error ratejudgement (CRC), and a judgement as to whether it is exceeding aprescribed error rate β or not is made (S910). In the case where it isexceeding the error rate β, the above described steps S901 to S906 arecarried out again, and in the case where it is not exceeding, thefrequency of occurrence of the error is counted (S909).

In the case where the consecutive number of times at which the errorframe occurred is less than the prescribed number of times na at thestep S909, the above described steps S903 to S906 are executed again. Onthe other hand, in the case where the consecutive number of times atwhich the error frame occurred is exceeding the prescribed number oftimes nα at the step S909, the already set values of the requiredsub-carrier number Ns and the optimum sub-carrier bandwidth Bs are leftunchanged, and only the optimum guard interval T_(G) is re-set (S908),and the processing of the above described steps S903 to S906 isexecuted.

In this way, it is possible to improve the frequency utilizationefficiency by reducing the guard interval in the case where thecommunication quality is good, and it is possible to attach the optimumguard interval length according to the propagation path.

Thirteenth Embodiment

Note that, in the seventh embodiment to the twelfth embodiment describedabove, the exemplary case of applying the transmission device of thepresent invention to the OFDM transmission scheme has been described,but the present invention is not limited to this, and it is alsopossible to apply it to the variable spreading-orthogonal frequency codedivision (VSF-OFCDM: Variable Spreading Factor-Orthogonal Frequency andCode Division Multiplexing) transmission scheme which is the fourthgeneration communication scheme, for example. In this VSF-OFCDM, theinformation symbol is divided on a plurality of frequency axes, and theinformation symbol is transmitted by spreading it by a spread code of avariable spreading rate which is assigned to each radio mobile station.

The transmission device according to the present embodiment has, asshown in FIG. 40, at the transmission unit 1100, a multiplexing unit1201 for multiplexing the transmission signals (information symbols) andthe pilot signals, a serial/parallel conversion unit 1202 for convertingthe multiplexed signals into parallel signals, a copying unit 1230 forcopying each signal sequence, a spread code generation unit 1209 forgenerating a spread code, a multiplication unit 1204 for multiplyingeach signal sequence copied by the copying unit 203 with the spreadcode, a combining unit 1205 for combining the multiplied signals, aninverse fast Fourier transform unit (IFFT) 1206 for applying the inversefast Fourier transform to the combined signals, a parallel/serialconversion unit 1207 for converting respective transformed signals intoa single signal sequence, a guard interval attaching unit 21, a data andcontrol signal combining circuit 19, a radio transmitter 6, amultiplexing control unit 1210, a transmission sub-carrier bandwidthcontrol unit 9, and a fading estimation unit 8.

The serial/parallel conversion unit 1202 is a circuit for converting theserial signals into parallel signals which are a plurality of signalsequences, according to the bandwidth and the number of sub-carrierscalculated by the transmission sub-carrier bandwidth control unit 9, andthe converted parallel signals are respectively outputted to the copyingunit 1203.

The copying unit 1203 is a circuit for copying each information symbolof a plurality of information symbol sequences which are serial toparallel converted at the serial/parallel conversion unit 1202 as manyas the number equal to the sequence length (chip length) of the spreadcode, and the copied information symbols are arranged on the frequencyaxis and outputted to the multiplication unit 1204 as one set of theinformation symbol sequence.

The spread code generation unit 1209 is a circuit for generating thespread code of a prescribed spreading rate which is assigned to eachradio mobile station as many as the number of sub-carriers, according tothe spreading rate inputted from the multiplexing control unit 1210. Themultiplication unit 1204 is a circuit for multiplying each informationsymbol copied at the copying unit 1203 with the spread code generated bythe spread code generation unit 1209.

The inverse fast Fourier transform unit 1206 is a circuit for carryingout the inverse fast Fourier transform on a plurality of signalsequences inputted from the combining unit 1205, according to thebandwidth and the number of sub-carriers calculated by the transmissionsub-carrier bandwidth control unit 9, and each transformed signalsequence is outputted to the parallel/serial conversion unit 1207.

The parallel/serial conversion unit 1207 is a circuit for converting aplurality of signal sequences inputted from the inverse fast Fouriertransform unit 1206 into serial signals which are a single signalsequence, according to the bandwidth and the number of sub-carrierscalculated by the transmission sub-carrier bandwidth control unit 9. Theguard interval attaching unit 21 inserts the guard interval into thesignals converted by the parallel/serial conversion unit 1207.

The multiplexing control unit 1210 calculates the modulation scheme andthe spreading rate, according to the propagation path state (fading)estimated by the fading estimation unit 8 and the transmissionsub-carrier bandwidth and the number of sub-carriers calculated by thetransmission sub-carrier bandwidth control unit 9, and outputs them tothe multiplexing unit 1201 and the spread code generation unit 1209.

Then, at the transmission unit 1100, the transmission signalsmultiplexed by the multiplexing unit 1201 are converted into theparallel signals formed by a plurality of signal sequences by theserial/parallel conversion unit (S/P) 1202, and after carrying out thecopying processing at the copying unit 1203, each signal sequence ismultiplied with the spread code generated by the spread code generationunit 1209, and after applying the inverse Fourier transform on thesecombined signals at the inverse fast Fourier transform unit (IFFT) 1206,they are converted into serial signals formed by a single signalsequence by the parallel/serial conversion unit (P/S) 1207, the guardinterval is inserted into these serial signals by the guard intervalattaching unit 21, each parameter calculated by the transmissionsub-carrier bandwidth control unit 9 is combined by the data and controlsignal combining circuit 19, and the OFDM signals are transmitted.

On the other hand, as shown in FIG. 40, the transmission deviceaccording to the present embodiment has a radio receiver 11, a data andcontrol signal separation circuit 20, a guard interval removing unit 22,a serial/parallel conversion unit 1301, a fast Fourier transform unit1302, a channel estimation unit 1307, a spread code generation unit1308, multiplication units 1303 and 1304, an adder 1305, aparallel/serial conversion unit 1306, a sub-carrier band informationextraction means 12, and a received sub-carrier bandwidth control unit13.

The serial/parallel conversion unit 1301 is a circuit for converting theserial signals into parallel signals which are a plurality of signalsequences, according to the bandwidth and the number of sub-carrierscalculated by the received sub-carrier bandwidth control unit 13, andthe converted parallel signals are respectively outputted to the fastFourier transform unit 1302. The parallel/serial conversion unit 1306 isa circuit for converting a plurality of signal sequences inputted fromthe adder 1305 into the serial signals which are a single signalsequence, according to the bandwidth and the number of sub-carrierscalculated by the received sub-carrier bandwidth control unit 13.

The channel estimation unit 1307 is a circuit for extracting the pilotsignals from the signals transformed by the fast Fourier transform unit1302, and estimating the channel variation value of each sub-carrieraccording to these pilot signals. Also, the multiplication units 1303and 1304 are circuits for guaranteeing the variation of each sub-carrieraccording to the variation value estimated by the channel estimationunit 1307 and multiplying the spread code generating by the spread codegeneration unit 1308.

Then, at the reception unit 1200, the sub-carrier band information isextracted by the sub-carrier band information extraction means 12according to the control signals separated by the data and controlsignal separation circuit 20 from the received OFDM signals, and theguard interval is removed by the guard interval removing unit 22. Atthis point, the received signal waveform acquired by the radio receiverand the fading time variation information and the delay distortionacquired at the data and control signal separation circuit 20 are sentto the fading estimation unit 8.

Next, they are converted into parallel signals formed by a plurality ofsignal sequences by the serial/parallel conversion unit (S/P) 1301,according to the sub-carrier bandwidth and the number of sub-carrierscalculated by the received sub-carrier bandwidth control unit 13according to the sub-carrier band information, and the Fourier transformis applied to each signal sequence at the fast Fourier transform unit(FFT) 1302. After that, each transformed signal is multiplied with thevariation value estimated by the channel estimation unit 1307 and thespread code generated by the spread code generation unit, and they areconverted into the serial signals formed by a single signal sequence bythe parallel/serial conversion unit (P/S) 1306, and these serial signalsare outputted as the demodulated signals.

According to such a transmission device according to the presentembodiment, the information symbol is divided on a plurality offrequency axes according to the propagation route (fading) state, andthe information can be transmitted by spreading it by a spread code of avariable spreading rate which is assigned to each reception device, sothat it is possible to multiplex signals of a plurality of users intosignals of the identical time in the identical frequency band, accordingto the propagation route for each reception device, and it is possibleto prevent interferences among users while realizing the efficientutilization of the resources.

Also, according to the transmission device according to the presentembodiment, the wide band system of the OFDM scheme and the narrow bandsystem can be made to coexist in the identical frequency band, so thatby using two schemes in the same frequency band together, the newgeneration communication scheme can be made to coexist, and in the caseof changing the communication scheme, a smooth transition in stages fromthe previous scheme to the new scheme can be made.

According to the radio communication system and the radio communicationmethod of the present invention, by calculating the optimum sub-carrieroccupied band according to the fading radio wave propagation pathinformation, and making the transmission band variable by adaptivelycontrolling the clock rate and the number of sub-carriers, even in thecase of carrying out the transmission of the identical information bitrate according to the fading time variation and the maximum delayamount, it is possible to realize the improvement of the transmissioncharacteristics by changing the optimum sub-carrier bandwidth and thenumber of sub-carriers of the OFDM according to the characteristics ofthe transmission path.

Also, the maximum tolerable bandwidth given to the system is constant,and the channels deviating from the system band occur in the case ofenlarging the sub-carrier occupied band, but the channel mapping controlfor not making the mapping to outside the system bandwidth is carriedout, so that it is possible to improve the utilization efficiency of thefrequency bands possessed by the system.

1. A radio communication system for carrying out communications betweenradio stations by modulating a plurality of signal sequences to betransmitted and received into at least one frequency channel assigned toeach of a plurality of cells, a radio communication system characterizedby having a channel mapping means for rearranging for each cell aplurality of frequency channels assigned with respect to each cell, andnewly assigning particular frequency channels as a transmission andreception band of said signal sequences, and a bandwidth control meansfor controlling a bandwidth of said assigned frequency channel accordingto a propagation state of said assigned frequency channel.
 2. The radiocommunication system as described in claim 1, characterized in that saidchannel mapping means is a means for carrying out communications betweenradio stations through the frequency channel assigned to each of aplurality of areas, and has a channel mapping circuit for carrying outrearrangement of assignment of said frequency channels, and assigningparticular continuous frequency channels of a system band for each ofsaid areas, and a converter for converting the frequency channelsrearranged by said channel mapping circuit into sub-carriers byorthogonal multiplexing.
 3. The radio communication system as describedin claim 1, characterized in that said bandwidth-control means is ameans for converting information data sequences into a plurality ofchannels, and transmitting and receiving a signal sequence of each ofthese plurality of channels by a plurality of orthogonalized sub-carriersignals, and has a fading estimation means for estimating a propagationroute of said sub-carrier signals, and a sub-carrier bandwidth controlmeans for controlling a bandwidth of said sub-carrier signals to betransmitted and received, according to a fading information estimated bysaid fading estimation means.
 4. A radio communication system forcarrying out communications between radio stations through frequencychannels assigned to each of a plurality of areas, a radio communicationsystem characterized by having a channel mapping circuit for carryingout rearrangement of assignment of said frequency channels, andassigning particular continuous frequency channels of a system band foreach of said areas, and a converter for converting the frequencychannels rearranged by said channel mapping circuit into sub-carriers byorthogonal multiplexing.
 5. The radio communication system as describedin claim 4, characterized in that it has a table memory device forstoring a search table indicating a using state of frequency channelsused in nearby areas, and said channel mapping circuit acquires saidsearch table and carries out a search of a vacant channel, andrearranges the frequency channels according to this search result andassigns continuous channels with respect to identical cell.
 6. The radiocommunication system as described in claim 4, characterized by having achannel selection device for generating unused frequency channels byrepeating rearrangement by said channel mapping circuit and theorthogonal multiplexing by said converter, and assigning new channels togenerated unused frequency channels.
 7. The radio communication systemas described in claim 4, characterized in that this radio communicationsystem has a hierarchical cell structure formed by a macro-cell andmicro-cells contained in this macro-cell, and in a case where thesemacro-cell and micro-cells use an identical frequency band, it has meansfor shifting a partition which is a boundary between a frequency channelband of the macro-cell and a frequency channel band of the micro-cells,and means for concentrating vacant channels before and after thepartition by carrying out rearrangement of the frequency channels bysearching vacant channels, using a shifted partition as a reference. 8.The radio communication system as described in claim 7, characterized inthat said shifting of the partition is carried out by giving a prioritylevel for each frequency channel according to a traffic state in saidmacro-cell and micro-cells, and rearranging the frequency channelsaccording to this priority level.
 9. The radio communication system asdescribed in claim 4, characterized in that a transmission scheme usedby this radio communication system is a scheme for spreading saidinformation symbol in a plurality of time regions or frequency regions,according to a spread code assigned to a terminal of a receiving side,and making a rate of the spread code with respect to said informationsymbol rate variable.
 10. In a signal transmission system for convertinginformation data sequences into a plurality of channels, andtransmitting and receiving a signal sequence of each of these pluralityof channels by a plurality of orthogonalized sub-carrier signals, aradio communication system characterized by having a fading estimationmeans for estimating a propagation route of said sub-carrier signals,and a sub-carrier bandwidth control means for controlling a bandwidth ofsaid sub-carrier signals to be transmitted and received, according to afading information estimated by said fading estimation means.
 11. Theradio communication system as described in claim 10, characterized byhaving a required number of sub-carriers control unit for calculating arequired number of sub-carriers that can be assigned to a user,according to a sub-carrier bandwidth controlled by said sub-carrierbandwidth control means, and branching a number of said plurality ofsub-carriers to be transmitted and received into the required number ofsub-carriers.
 12. The signal transmission system as described in claim11, characterized in that said required number of sub-carriers controlunit has a function for calculating a total bandwidth to be assigned tothis user from a required information bit transmission speed of theuser, and calculating the required number of sub-carriers from saidtotal bandwidth and an optimum sub-carrier bandwidth informationcalculated by said sub-carrier bandwidth control unit.
 13. The radiocommunication system as described in claim 10, characterized in thatsaid fading estimation means generates a fading time variationinformation and a delay distortion information in a radio wavepropagation path, according to a waveform of received signals, andestimates said propagation route according to these information.
 14. Theradio communication system as described in claim 10, characterized byhaving a signal composition unit for transmitting the fading informationestimated by said fading estimation means by multiplexing it with a userdata information, and a signal separation unit for separating saidfading information from a received data matrix.
 15. The radiocommunication system as described in claim 10, characterized by having ameans for detecting a sub-carrier bandwidth information according tosaid fading information, a clock control means for calculating a clockfrequency from the detected sub-carrier bandwidth information, a meansfor converting a frequency generated by a clock oscillator into theclock frequency calculated by said clock control unit, and carrying outserial to parallel conversion at the clock frequency according to thissub-carrier frequency, and a channel selection means for selecting adesired channel from a single or plurality of sub-carrier channels afteran inverse discrete Fourier transform.
 16. The radio communicationsystem as described in claim 10, characterized in that a transmissionscheme used by this signal transmission system is a scheme for spreadingsaid information symbol in a plurality of time regions or frequencyregions, according to a spread code assigned to a terminal of areceiving side, and making a rate of the spread code with respect tosaid information symbol rate variable.
 17. A radio communication methodfor carrying out communications between radio stations by modulating aplurality of signal sequences to be transmitted and received into atleast one frequency channel assigned to each of a plurality of cells, aradio communication method characterized by having (a) a step forrearranging for each cell a plurality of frequency channels assignedwith respect to each cell, and newly assigning particular frequencychannels as a transmission and reception band of said signal sequences,and (b) a step for controlling a bandwidth of said assigned frequencychannel according to a propagation state of said assigned frequencychannel.
 18. The radio communication method characterized in that saidstep (a) is a step for carrying out communications between radiostations through the frequency channel assigned to each of a pluralityof areas, and has (a1) a step for carrying out rearrangement ofassignment of said frequency channels, and assigning particularcontinuous frequency channels of a system band for each of said areas,and (a2) a step for converting the frequency channels rearranged by saidchannel mapping circuit into sub-carriers by orthogonal multiplexing.19. The radio communication method characterized in that said step (b)is a step for converting information data sequences into a plurality ofchannels, and transmitting and receiving a signal sequence of each ofthese plurality of channels by a plurality of orthogonalized sub-carriersignals, and has (b1) a step for estimating a propagation route of saidsub-carrier signals, and (b2) a step for controlling a bandwidth of saidsub-carrier signals to be transmitted and received, according to afading information estimated by said step (b1).
 20. A radiocommunication method for carrying out communications between radiostations through frequency channels assigned to each of a plurality ofareas, a radio communication method characterized by having (a1) a stepfor carrying out rearrangement of assignment of said frequency channels,and assigning particular continuous frequency channels of a system bandfor each of said areas, and (a2) a step for converting the frequencychannels rearranged by said channel mapping circuit into sub-carriers byorthogonal multiplexing.
 21. The radio communication method as describedin claim 20, characterized in that the rearrangement of channels by saidstep (a1) is carried out with respect to parallel output signalsequences of an identical symbol rate.
 22. The radio communicationmethod as described in claim 20, characterized in that the rearrangementof channels by said step (a1) is carried out with respect to paralleltransmission baseband signal sequences corresponding to a plurality ofusers.
 23. In a signal transmission method for converting informationdata sequences into a plurality of channels, and transmitting andreceiving a signal sequence of each of these plurality of channels by aplurality of orthogonalized sub-carrier signals, a radio communicationmethod characterized by having (b1) a step for estimating a propagationroute of said sub-carrier signals, and (b2) a step for controlling abandwidth of said sub-carrier signals to be transmitted and received,according to a fading information estimated by said step (b1).
 24. Theradio communication method as described in claim 23, characterized bymaking a setting regarding an optimum sub-carrier bandwidth, a requirednumber of sub-carriers, and a guard interval according to said fadinginformation, at a time of communication start.
 25. The radiocommunication method as described in claim 23, characterized by making asetting of a guard interval length according to said fading information,periodically at a prescribed time interval determined in advance. 26.The radio communication method as described in claim 23, characterizedby making a setting of a guard interval length according to said fadinginformation, in a case where an optimum sub-carrier bandwidth, arequired number of sub-carriers, a guard interval, or a signal errorrate becomes less than or equal to a certain reference.